Tom Brady, Sofia Vergara, J Balvin, and Dakota Johnson aren’t the ones footing the bill for all the recent summer yacht parties … the honor actually goes to a billionaire businessman, TMZ has learned.

Sources with direct knowledge tell TMZ … the lavish yacht that’s been bopping around the Mediterranean all season isn’t rented or owned by the famous faces onboard.

Our sources say it’s Israeli-Canadian businessman billionaire Mark Scheinberg‘s personal floating palace — and he’s the one treating his famous friends to sun, surf, champagne … and some sexy fun.

Along for the ride on all these star-studded parties on the sea are Mark’s friends, as well as best friend, Doug Chabbott. We’re told Mark and Doug love hanging with celebs and always extend invites for yacht hangouts.

As we reported … Tom and Sofia are having a summer fling … but aren’t dating. It all started while they were out at sea on a trip through Europe, where the two have been spotted on Scheinberg’s yacht.

Last week, Dakota was also seen partying with the crew — and speculation started building about a “mystery man” by her side on the yacht. That was Doug … and no, we’re told they’re not dating. They’re just friends who met on the yacht after the invitation was extended.

One source claims not every celebrity has said yes to their invitation. They’ve been turned down by some stars who thought it was odd being they didn’t know Mark or Doug.