Actor Victor Webster (“Melrose Place”) will guest star on ABC’s “Castle,” playing new boyfriend to Kate Beckett (Stana Katic). In the episode entitled “Punked” (airdate TBD), Josh Davidson (Webster) surprises Beckett by coming to the precinct to pick her up. On seeing the big and sexy Davidson, the gang wonder: Who the hell is that guy? “Castle” will premiere Monday, September 20 (10:00-11:00 p.m., ET) on ABC.