HBO’s “Game of Thrones” will return for its third season on March 31, 2013.Much-anticipated premiere date was announced before a crowd of gleeful fans at Comic-Con in San Diego. Season two of the fantasy drama recently concluded on June 3. In other “Thrones” news divulged at the panel, Diana Rigg and Mackenzie Crook will be joining the cast. Other new thesps to come on board include Clive Russell, Nathalie Emmanuel and Kerry Ingram. The panel was moderated by George R.R. Martin, author of the books for which the show is based. Others taking part in the festivities were current castmembers Richard Madden, Michelle Fairley, Emilia Clarke and Alfie Allen, as well as exec producer Carolyn Strauss.