What's behind the casting of David Duchovny in an upcoming guest arc on ''Sex and the City''? Well, as executive producer Michael Patrick King told the New York Daily News regarding the former ''X-Files'' star: ''Who more perfect to be on a show riddled with handsome exes?'' Funny, but which of the four femmes is he going to romance? Will he be the much-touted rival for Big (Chris Noth) as the series winds down, after Carrie (Sarah Jessica Parker) presumably gives current beau Berger (Ron Livingston) the boot? The truth is still out there, since King wouldn't say. But he did recently tell TV Guide Online that HBO had cast ''a big name'' as Big's competition. Which means that it's far from certain that Big will wind up with Carrie when the series ends in early 2004. ''Why would we bring in a major name if [Big] was already [the clear winner]?'' King told TV Guide Online.
As if that weren't confusing enough, another love interest is joining the cast this summer. It's Duchovny's ''Full Frontal'' costar Blair Underwood. Producers aren't saying which of the gals the onetime ''L.A. Law'' hottie will romance, though Carrie's dance card seems awfully full, and Charlotte (Kristin Davis) seems to be in it for the long haul with Harry (Evan Handler), seeing how she's converted to Judaism to marry him. Guess that leaves Samantha (Kim Cattrall) or Miranda (Cynthia Nixon), though the former is currently having a fling with a boytoy actor/waiter, and the latter is involved with her TiVo. Last seen opposite Jamie Kennedy in ''Malibu's Most Wanted,'' Underwood begins his four-episode guest stint in August.