The feeling I have before meeting Jeff Koons, the extravagantly successful American artist, is reminiscent of the sense of defeated curiosity I experienced some years ago on the way to interview Gilbert and George. It's the strong suspicion that I'm going to be the recipient of a performance and that nothing I ask or say is likely to affect or alter that performance.  The comparison, it turns out, is both fair and misleading. While Koons does give the impression of a slickly rehearsed act, and there are superficial similarities to G&G – the habitual suit-wearing, the faultless good manners – there is also something quite different about Koons's manner. Where the British pair were elusive, teasing and almost metronomically detached, the American is open, earnest and as innocent as a white-picket fence.  The question, however, remains essentially the same: is he for real?  First, there is the peculiar nature of the art: giant childlike inflatables, a huge topiary puppy, kitsch figurines that look as if they've walked off the advertising pages at the back of the Sunday Telegraph and, most notoriously, the explicit sexual poses of himself and his ex-wife, the former porn actress La Cicciolina, that featured in his series Made in Heaven. If that was not enough, Hanging Heart, his stainless-steel hanging sculpture of a birthday-card heart, set a world record for a living artist in 2007 when it sold for $23.6m.  Then there is the no-less-anomalous quality of the man – the softly spoken one-time commodities broker who combines an acute financial acumen with a kind of hokey sense of wonderment. The art critic Matthew Collings once described Koons's "pleasant cartoon-like face" as "part classic American handsome, part Mad magazine". The handsomeness has since relinquished territory, and hair, to the caricature.  It's been 25 years since he first came to prominence. He's now 56 and the intervening years, while commercially profitable, have not always been kind. Nor have the critics. The harshest judgment came from Robert Hughes, who saw in Koons a sanctimonious intimacy with corporate fashion. "He has the slimy assurance, the gross patter about transcendence through art, of a blow-dried Baptist selling swamp acres in Florida," wrote Hughes in 2004.  Still, the major setback in Koons's life has had nothing to do with critical opinion, but it is the reason I'm visiting the artist on a hot New York morning at his studio-cum-factory in an urban blank spot west of Manhattan's Chelsea district. In 1994, Koons's then 18-month-old son, Ludwig, was taken by his mother, Ilona Staller (aka La Cicciolina) to Italy in contravention of a New York court order. Despite a bitter and protracted legal battle, Koons was unable to regain custody of his son, who remains in Rome. Right from the start he viewed his son's removal as child abduction and sought the help of Ernie Allen, the president of the International Centre for Missing and Exploited Children (ICMEC). From the resulting relationship, Koons decided to set up the Koons Family Institute on International Law and Policy, which is tasked with providing data and analysis for the ICMEC.  Enter Kiehl's, the American cosmetics company, for which Koons has designed a special-edition bottle top in the shape of his sculpture Balloon Flower. Proceeds from the sale of the limited-edition "Creme de Corps" – estimated to be $200,000 – will go to the Koons Family Institute. Hence Koons is promoting the philanthropy-as-marketing-strategy by talking about his own experience as a victim of child abduction.  First, though, he shows a group of journalists from Europe and Korea around his studio. It's a huge, white, light-filled space in which 25-30 young artists are quietly but industriously engaged in work on a series of large paintings depicting Aphrodite, Pan and Eros. The painting has been pre-bought by Bill and Maria Bell, part of the soap-opera dynasty responsible for such imperishable daytime series as The Bold and the Beautiful and The Young and the Restless. "The Bells are fantastic," says Koons. "They're great collectors."  He talks about an image of the actor Gretchen Mol sitting on an inflatable dolphin. "It really felt mythological to me. Art's a very intuitive process and its vocabulary is very intuitive, very connecting, very archetypal. Information is profound and communal." The Koreans don't seem to have any more idea of what he's talking about than I do, but nor do they appear particularly concerned, posing for photographs with him as he mugs for the camera.  "I enjoy readymades," Koons goes on. "It's a way that I can communicate a form of acceptance, that everything is perfect. It's about accepting ourselves and accepting others."  Koons tends to talk about art in a kind of readymade language, running together words and concepts that sound meaningful without always placing them in a sequence that is meaningful. But just when you're ready to let it all slide to the back of your mind, he'll slip in a genuine insight. I asked him, for example, about beauty, a quality he frequently refers to when discussing his works, or at least their inspiration.  "I would have to say what I find beautiful in the world is the moment that has been revealed, that something is brought into the light. And it only comes from being human, this process of unveiling, if we can open ourselves up to our possibilities." Or as he once put it: "If I think of the word beauty, I think of the word vagina… or the ass." He was talking then in the context of Made in Heaven, which featured a piece called, with forensic accuracy, Ilona's Asshole. It was in the creation of this work, of which he remains extremely proud, that his parental problems began.  The day after THE TOUR, Koons and I are sitting with Ernie Allen, who is a 65-year-old lawyer and Southern gentleman of the old school, in the middle of the studio, while Koons runs through his story from the beginning. It starts on an autostrada in Italy, where Koons found himself looking at porn magazines. For artistic reasons, of course.  "I acquired them so I could show my production people," he recalls. "If you pick up a Vogue or a Cosmopolitan, you really don't see much flesh. You'll see a hand or an arm, but you don't see what the back looks like. I came across my ex-wife's photographs and I was moved by the fantasy of the photographs. They were like a fairy tale in a way. I guess Eastern European eroticism."  I make sure not to catch the eye of Allen, who has just completed a 15-minute explanation of what his centre has done to combat child pornography – a different category entirely, of course, but not so different that he'd be the first person with whom I'd want to discuss the aesthetic merits of Ilona's Asshole.  In 1989 the Whitney Museum asked Koons to make an artwork about the media. He'd just finished his Banalities series, which included a sculpture of Michael Jackson with his ape Bubbles, and he was the toast of the New York art world.  "I thought as a readymade I will call this woman up, this Italian politician, and I'll just place myself in these sets," he recalls. "And it will be like we made a film. And I thought the next level of stardom in American culture is film, because I've always believed that you weren't viewed as participating in culture unless you were in Hollywood. But of course this is just advertising a film that doesn't exist."  So he called up Staller, star of such adult fare as Il Pornopoker and Dog Lay Afternoon, who traded on her sexual notoriety in the 1980s to become a politician in Italy. Her most memorable contribution to international politics was her offer before the beginning of the first Gulf War to have sex with Saddam Hussein if he would return the foreign hostages he was holding. Koons employed her as a model in the shoot that formed the basis of the resulting work for the Whitney.  "And we flirted a little bit with each other," he continues in the same careful tone, as though recalling a particular artistic detail. "I found Ilona a very, very beautiful woman. I was curious about her, you know, being in politics in Italy. And she presented herself to me as a victim of pornography when she was younger in Hungary. They had no food; she had to bring home money. I went back and we did another photo session and we ended up falling in love. I was kind of living this philosophy: embrace your past. You know, I was naive to think that somebody could be involved in certain areas and then just let go of that completely."  He says that he often asked himself: "Jeff, what are you doing?" but he quashed his doubts and threw himself into the relationship. Still skirting Allen's gaze, I ask Koons if he found the experience liberating in any way.  "I think so," he says matter-of-factly. "Ilona was absolutely very comfortable with her body, so that was a very liberating aspect for me."  The couple moved to New York, married in 1991, and Ludwig was born in 1992. The following year they separated. "When it started to become clear to me that I'd got myself involved in something much more complex than I had any idea of, I tried to take action to protect my son," says Koons. "That's why I filed for divorce."  But Staller fled to Rome with Ludwig, and it would be three months before Koons located the whereabouts of his son. "I always felt that I would get him to be returned to New York because we had shared custody at the time and he wasn't allowed to be taken out of the jurisdiction," says Koons, sounding as guileless as the scarecrow from The Wizard of Oz. "And I really believed in a system in which people would automatically do the right thing. But that did not happen."  Instead he had to go to Italy. He says he fought for years to get his son returned. "In the beginning, after months and months of trying, I was eventually able to see my son, but only for an hour and a half a day under armed guard. Eventually I was able to take my son outside his home in Rome, but under armed guard – people assigned by my ex-wife."  "Let me interject here," says Ernie, now that we were back on the more secure terrain of child abduction. "This wasn't Syria. This was a western democracy. It was Italy. It really illustrated that this was a really complex problem. Even when you had clear legal right and authority, you couldn't get your kid back."  "I mean, my son was really just turned against me," Koons continues. "I don't have a relationship with my son today. Maybe out of the blue I'll get a phone call from him and then I won't hear from him for another year. There's just no relationship there."  Koons says the legal costs drove him to the verge of bankruptcy, though others have attributed his precarious financial position in the mid-90s as much to his fanatical perfectionism and the vast scale of his Celebration series. One of the things that brought him back from the brink, at least psychologically, was his reunion with his daughter Shannon, who was conceived when he was a student at Maryland Institute College of Art. He says he offered to marry Shannon's mother when she became pregnant, but she thought they were too young for that commitment.  So the girl was put up for adoption, and a broken-hearted Koons left Maryland because it was, he says, too painful to remain. He thinks the adoption helped galvanise a desire to become famous. "I think I was always ambitious," he says. "I think I always wanted to participate in the dialogue of art. But I think that it helped make me want to have more visibility so that my daughter could find me. I always hoped that we could reconnect."  They did in 1995, and Koons has subsequently built what he describes as a "very close relationship" with Shannon, her husband and their two daughters – his granddaughters. He also has five other children by his second wife, the artist Justine Wheeler, who once worked as one of the hired hands at his studio.  He is now not just financially secure but deeply settled, and consequently at ease with the world, even if he still appears – at least to those who don't know him – slightly estranged from himself. He's given to voicing the kind of soft-hearted platitudes that are not normally associated with conceptual artists who graphically depict their lover's genitalia, such as: "Family life is the most important thing to me" and that all that matters in life and art is "actual human interaction".  I wouldn't describe my interaction with Koons as the most full-blooded and humanising encounter of my life, or even week, but I nonetheless came away with an improved opinion of him. For all his arty sales patter, his befriending of wealthy collectors and his mannered sincerity, there is something unmistakably genuine about Koons. No artist could make him up. Not even Jeff Koons himself.
When Jeff Koons married porn star La Cicciolina the world gasped. But then she fled to Rome, and the artist lost all hope of a relationship with his son. Here he talks to Andrew Anthony about his work, heartache and a strange love that soured