New dad William was spotted with his pals, including his close friend Guy Pelly, at Paddington train station on Friday. The group headed to Exeter St Davids in a private carriage where they will celebrate with the groom-to-be.
"I walked through the carriage on the way to the buffet car and spotted William with a bunch of chaps swigging beer like it was going out of fashion," a member of the public told the Sun. "The tables were covered with cans and miniature bottles of gin and one chap seemed to be wearing gold lamé shorts."
The Duke of Cambridge, who was dressed smartly in chinos and a shirt, headed back to North Wales last week to return to his job as a Royal Air Force search and rescue pilot.
The Prince's two-week paternity leave is now over meaning William had to leave Kate and George at Carole and Michael Middleton's home.
But mother and son are expected to make the 270 mile trip to North Wales "at some point" over the coming weeks so proud William can introduce his son to his colleagues.
The 31-year-old Prince took some time out from his duties as a new dad last weekend when he took part in a charity polo match in Berkshire, near the Middleton's family home in Bucklebury.
After leading his team to victory William was presented with a miniature polo mallet which was a gift for baby George.