Did you hear the one about Aaron Spelling recruiting Shannen Doherty’s Beverly Hills, 90210 replacement, Tiffani Thiessen (left), to step in for the exiting Doherty next season on Charmed? Turns out that’s no joke. ”Tiffani was our first choice to take over for Shannen — even before we asked Jennifer [Love Hewitt],” Spelling tells EW. ”But Tiffani told us she wants to do a half-hour comedy.” (Alas, NBC didn’t pick up her sitcom pilot.) Since Spelling’s big-name choices have taken a pass — Hewitt likely wants to focus on films — the Uberproducer says the show is leaning toward a fresh face to play a younger witch in the Halliwell household. ”She’s going to be the long-lost little sister Alyssa [Milano] and Holly [Marie Combs] never knew they had. And wait until you see what we came up with to explain why she’s been lost: Nobody ever knew she even existed.” Spelling says producers are recutting last month’s season finale to explain the sudden disappearance of Doherty’s Prue. Our guess: She’s locked away in a behavioral-therapy clinic with Brenda Walsh.