Prince William's Belated Birthday Bash on the Beach With Kate Middleton and Prince Harry

Duke of Cambridge enjoys some sand and surf with family and friends to celebrate turning 30

For Prince William, life's a beach.

The future king certainly made up for last Thursday's low-key 30th birthday celebration by hitting the sand and surf over the weekend.

"He had a bunch of friends staying with him in his rented cottage in Anglesey," a source tells E! News. "On Saturday, they all got up quite late, had breakfast at the house and then loaded up a car with an inflatable donut and drove down to the beach."

Once there, Prince William and several other young men, including brother Prince Harry, slipped into their wet suits.

"They had a boat, and they attached the donut to it and they all got in and had a ride," the source adds. "William was in it, Harry was in it. It looked like fantastic fun."

Also on hand?

Wills' lovely wife, Kate Middleton, who opted to keep dry by hanging out with sister Pippa and their pals on the sand.

"They had [Prince William and the Duchess of Cambridge's dog] Lupo with them and they were playing with him," the source says. "They were wearing Wellies [Wellington boots] and bundled up as they chatted" since the weather was a bit chilly.

The party of 12 eventually left the beach "around 1:30" and headed back to the cottage.

No word, though, on what the group did later that day.