In Palmer on Thursday, at about 03:00 an officer told Karen and Jay Priest their son Justin, 29, had been killed.
The devastated couple drove to Justin Priest's girlfriend's home to inform her, when he greeted them at the door.
In fact, another man with the same name but different birthday was killed. The Juneau police apologised for the error.
After hearing the horrible news, the Priests telephoned far-away relatives, then drove to Anchorage to tell their other son in person, they told Alaska Dispatch News.
Then, the grieving family set out to inform Justin's girlfriend of five years.
At her home at about 05:30, Justin Priest said he heard a knock on the door as he was getting ready to walk his dog. Still bleary-eyed from sleep, he was surprised to see his family. All erupted with joy, praising Jesus and embracing one another in tears.
"It opens and right here is Justin. I don't even see it but Jay is sobbing. It doesn't compute to me. Then I see him," Mrs Priest told the Associated Press news agency. "You want it to be true, but you go, 'Am I hallucinating?' Justin didn't know what was going on."
The Juneau police have apologised for the anguish, however momentary.
Justin Priest told the Alaska Dispatch that the family's relief and joy is tempered by the awareness another family lost a son.

There were more than 2,000 family doctors in September 2014, excluding registrars, retainers and locums working in around 460 practices.
Health Minister Mark Drakeford said the statistics showed Welsh ministers' "commitment to invest in our NHS".
But Plaid Cymru highlighted a 1% fall in GP numbers from 2013/14, warning a "recruitment crisis is looming".
Plaid health spokeswoman Elin Jones said the fact that 23% of GPs were aged 55 or over and nearing retirement age needed to addressed.

James Moore, from Tullymore road in the Waterside, was due in court on Friday for driving without insurance, tax, L-plates and without a qualified driver.
The 24-year-old then texted his solicitor to request a postponement.
"Tell him to go easy on the paella and cerveza because his fines are going up," said the judge.
Judge Barney McElholm asked what was to stop Mr Moore dropping his driving licences in to his solicitor office before going on holiday.
"I will expect to see him in court in three weeks' time with his driving licence and glowing with a tan," said the judge.
The sentencing of Mr Moore, who committed the offences in February, was adjourned until 23 June at Londonderry Magistrates' Court.
Police in a small Alaska town mistakenly told a couple their son had been killed in a car crash, leading to an extraordinary reunion hours later.
[NEXT_CONCEPT]
The number of GPs in Wales rose overall by 10.5% in the 10 years to 2014, according to new figures.
[NEXT_CONCEPT]
A Londonderry motoring offender has missed his court sentencing to go on a surprise Spanish holiday with his grandmother.