While recently appearing on Live! With Kelly, the actor, 44, revealed his four-year-old little boy palled around with Prince George and Princess Charlotte in London while Ben was shooting his latest movie, Justice League.
"It rains a lot in London... so they have those indoor play parks. So I took my son to one of those... and I get in there and I get this weird, stiff vibe and there's all these guys in there [wearing] suits. [So I think], 'Oh, it's dad's day at the Gymboree!' Ben began.
George, Charlotte and Samuel (inset). (Photo Credit: Getty Images, Splash)
"It turned out they were security guards and the kids who were playing in there were the royal kids," he continued. "So I can tell my son [one day] he played kickball with the King of England!"
Ben and his estranged wife, Jennifer Garner — who are also parents to two older daughters, Violet, 10, and Seraphina, 7, together — welcomed Samuel in February 2012.