We loved her as Brenda Walsh in the original "Beverly Hills, 90210," now Shannen Doherty 's back for multiple episodes of The CW's spin-off, "90210," including the two-hour premiere on Tuesday, September 2 at 8 p.m. -- and ET has your first look at scenes from the debut night! In the episode, West Beverly Hills High School has approached Brenda -- last seen headed to London to study acting -- to return to her alma mater as a guest director for the school's musical ...