In the recent HBO film “Confirmation,’’ concerning Anita Hill’s sexual harassment allegations against Supreme Court nominee Clarence Thomas, late Senator Ted Kennedy was played by Treat Williams. Now it’s Matthew Perry’s turn to portray the youngest of Joseph Kennedy’s three sons. The actor best known for his work on the sitcom “Friends’’ has been cast as Ted Kennedy in the Reelz miniseries “The Kennedys: After Camelot,’’ which is shooting now in Toronto. In the series, about the famous family’s travails following JFK’s assassination in 1963, actress Kristen Hager (pictured with Perry) stars as Joan Kennedy, Katie Holmes plays Jackie Kennedy Onassis, and Brett Donahue is John F. Kennedy Jr.