Shock jock Howard Stern, who bragged of his marital fidelity while entertaining scores of strippers and porn stars on his radio show, has split with his wife of 21 years. Stern and wife Alison, whose romance was the basis of his 1997 film “Private Parts,” are parting as friends, said Dan Klores, the couple’s spokesman. “Following mediation, both Alison and Howard, who care for each other very much, have amicably separated,” Klores said. The statement made no mention of a divorce, but some observers are noting that the fact that a mediator was involved signals the eventuality of an expedient divorce. The Sterns have three daughters, ages 16, 13 and 6. Howard’s earnings last year are reputed to have been $20 million.