The Duke of Cambridge turned 30 away from the public eye.
But while the milestone birthday was private, it certainly wasn't uneventful.
Prince William, an avid water sports fan, spent his big day zipping across the freezing sea near his home in Anglesey, Wales, the Sun reports.
The Duchess of Cambridge is said to have organised for a speed boat to pull her husband along the water in a rubber ring known as a 'doughnut' as a fun gift.
Despite the bad weather conditions, the second-in-line accepted the challenge with gusto as his wife, brother Prince Harry and friends including Thomas van Straubenzee, pictured below with Kate, "roared with laughter."
"For most 30-year-olds who have just inherited £10 million, the last thing they would want to do is freeze themselves on a wet weekend in Wales. But this is typical of William," a source told the newspaper.
After the icy dip, the royal party headed on to the couple's cosy cottage to toast the birthday boy with a hearty, home-made dinner.
While the Duke's big day was a down-to-earth affair, it was interspersed with gifts fit for a prince.
On turning 30, he received £10 million from his late mother Princess Diana's estate.
And the Queen gave him and his wife one of the cottages on her sprawling 20,000 acre Sandringham estate.