Newlywed Gwyneth's Cheating Secret Exposed!

Blabbermouth Spills Beans at Party for Bride & Groom.

NEWLYWEDS Gwyneth Paltrow and Brad Falchuk first got cozy while married to other people!

That racy tidbit was revealed at the couple’s rehearsal dinner — and The National ENQUIRER has learned it had guests cringing in embarrassment!

According to an on-scene spy, a loose-lipped guest dropped the cheating bombshell while giving a toast at funnyman Jerry Seinfeld’s home in the Hamptons.

“The speaker mentioned how Brad and Gwyneth first met when she sat on his lap on the set of ‘Glee,’ but everyone knew that was when they were both married to other people,” snitched the source.

“It was super awkward, and everyone looked around to make sure her kids weren’t there to hear it.”