Brian Austin Green confirms he hooked up with these '90210' co-stars

Brian Austin Green is setting the record straight about which co-stars he hooked up with during his Beverly Hills, 90210 days.

The 46-year-old actor stopped by Watch What Happens Live Thursday night, where a called asked him if he and Tori Spelling ever hooked up during the original run of the series.

"We hooked up. We did," he confirmed after hesitating and learning that Spelling had already admitted to the tryst. "... We were young, so that's what young people do."

Though he denied ever hooking up with fellow co-stars Shannen Doherty, Jennie Garth and Gabrielle Carteris, there was one other 90210 cast member Green, who is now married to actress Megan Fox, got busy with.

"Tiffani and I were dating before she started doing the show," he said of Tiffani Thiessen, who joined 90210 in season five.

As for why Thiessen isn't a part of BH90210 -- the reunion series that recently premiered on Fox -- Green explained that it was simply because "the reboot was the original cast and she wasn't in the original cast."

"That was sort of our idea going back, it was the original group of people that were there at the start," Green said.

ET's Kevin Frazier recently caught up with Green, and he opened up about how the reunion series planned to pay tribute to Luke Perry, an original cast member who died earlier this year.

"He'll be honored in a very respectful way," he said. "But to everybody that's ever met him or knew him, he was an amazing person and he was a blessing for people to have in their lives. And I feel so blessed I got to do what I did with him. That I had the experience that I did."