Sean, Robin & Petra Together at Cannes

Usually, when an estranged husband and wife begin to repair their damaged marriage, the last thing they do is go somewhere they're likely to run into the hubby's most-recent lady friend. And yet that's precisely what Sean Penn and Robin Wright Penn did on Saturday night when they attended a party hosted by Petra Nemcova at Nikki Beach in Cannes.

Supermodel Petra, who was rumored to have dated Sean after he and his Forrest Gump-star spouse separated in December, was on-hand at Nikki Beach to announce her latest project, a documentary about the meaning of love. Meanwhile, Sean and Robin attracted a ton of attention when they swept into the venue, where they joined Bono in a covered VIP area.

Witnesses inside the A-list bash say Petra eventually headedinto the VIP section, where she hugged and greeted the once-again happy couple. "Surprisingly, there didn't appear to be any tension as they all sat and comfortably chatted," one witness tells OK!. "Though Petra's interaction with Robin was limited. I didn't see them talk beyond their initial greeting."

According to the source in the party, Sean actually got up from his seat next to his wife at one point to sit on the armrest of Petra's seat and chat with her. "They had their own pretty long conversation, while Robin chatted with Bono," explains the insider. "Once Petra made her announcement about the documentary, Sean and Robin were back together."

The Penns left shortly after Petra made her speech, and it wasn't much later that the charity-minded beauty jumped onto a small boat to make her way out of the venue.