Brian Austin Green Was Jealous During Ex Tiffani Thiessen's Sex Scenes

Brian Austin Green admitted that jealousy on the set of "Beverly Hills, 90210" played a real hand in the demise of his past romance with fellow costar Tiffani Thiessen.

The actor made the confession during Monday's episode of Shannen Doherty's 'Let's Be Clear' podcast ... telling his ex-castmate all the deets about his split from the "Saved by the Bell" alum.

According to BAG ... TT was his first serious relationship -- as they dated between 1992 and 1995. However, when Tiffani joined Brian's teen drama during season 5 ... he admitted to getting incredibly jealous whenever his lady worked with other '90210' stars.

He told Shannen that he found it weird when his girlfriend all of a sudden had to do sex scenes with his friends -- whom he says he considered family.

Tiffani played Valerie Malone -- the ultimate bad girl who slept with almost all of the male leads ... except for Jason Priestley's Brandon Walsh.

As Brian tells it -- jealousy got the better of him and the pair split only a year after moving in together. Brian -- who is now engaged to "Dancing With the Stars" pro Sharna Burgess -- confessed that he was in the wrong and shouldn't have freaked out the way he did.

Thankfully, Brian and Tiffani were able to remain friends in the aftermath of their split -- which can't be said for other notable costar exes. Tiffani found her happy ending with actor Brady Smith -- they share kids Harper and Holt together.

Brian has obviously been in a handful of serious relationships since, previously welcoming kids with exes Vanessa Marcil and Megan Fox.