The following century, King William III's massive rebuilding and expansion project intended to rival Versailles was begun. Work halted in 1694, leaving the palace in two distinct contrasting architectural styles, domestic Tudor and Baroque. While the palace's styles are an accident of fate, a unity exists due to the use of pink bricks and a symmetrical, if vague, balancing of successive low wings.
Along with St. James's Palace, it is one of only two surviving palaces out of the many owned by King Henry VIII.
Information from Wikipedia which gives more detail.