Far from the cameras of the U.K.'s voracious press, the prince bid his single life goodbye in a bachelor party reportedly held in eastern England over the weekend.
Palace officials confirmed Monday only that the stag party - reportedly thrown by his brother and best man, Prince Harry - had taken place.
"It has happened," a spokeswoman said, speaking on condition of anonymity in line with palace policy. "We are not giving any details."
Those details have been the subject of intense speculation since William announced his engagement to 29-year-old Kate Middleton. The pair will wed April 29 at London's Westminster Abbey.
Would the party be held in Scotland or South Africa? Would there good old-fashioned British boozing? And would Harry, William's sometimes wayward younger brother, organize some spectacularly off-color prank?
The world may never know. The Daily Telegraph, which broke the news, said the prince and about 20 friends attended a weekend party thrown by Harry, possibly at an estate in Norfolk owned by the father of one of the guests.
The paper said the guests had been sworn to silence, quoting Thomas van Straubenzee, one of the likely partygoers, as saying: "I'm very sorry but I have got to keep it a secret. I hope you understand."
The party - thrown just before Harry was due to leave for a fundraising expedition to the Arctic - will have disappointed the paparazzi. The princes' social lives have filled hundreds of pages of tabloid print and British media in particular have made a mint off of Harry's penchant for partying.
A 2008 royal bachelor bash thrown in honor of Peter Phillips, William's cousin, was tabloid gold dust, yielding tales of drunken escapades across the Isle of Wight and even - it is alleged - a grainy picture of an exposed royal posterior.
The British media has also speculated often about Middleton's bachelorette party plans, with one tabloid reporting that her sister Pippa will be throwing a "Dirty Dancing"-themed hen party bash at the family home in the wealthy village of Bucklebury.
