K-9 and Company was a proposed television spin-off of the original programme run of Doctor Who. It was to feature former series regulars Sarah Jane Smith, an investigative journalist played by Elisabeth Sladen, and K-9, a robotic dog. Both characters had been companions of the Fourth Doctor, but they had not appeared together before. A single episode, "A Girl's Best Friend", was produced as a pilot for a proposed programme, but was not taken up. "A Girl's Best Friend" was broadcast by BBC1 as a Christmas special on 28 December 1981. The story was released on DVD on 16 June 2008 as a double pack with K-9's first Doctor Who story "The Invisible Enemy". Although a full series of K-9 and Company was not produced, the two characters did re-appear two years later in The Five Doctors, an episode of Doctor Who broadcast in 1983 celebrating the show's twentieth anniversary. Following the successful revival of Doctor Who in 2005, Sarah Jane Smith and K-9 would be re-introduced to the show in the second series episode "School Reunion", which aired in 2006. In addition to subsequent appearances by both characters in the main programme, this became the basis for another series featuring the two characters, The Sarah Jane Adventures, which debuted in 2007. K-9 appears only occasionally in the first and second series, and becomes a regular character in series three. Another unrelated programme, not produced by the BBC and without Sarah Jane, K-9, began airing in 2010. This series, created by one of the originators of the K-9 character, features a different version of the robot dog.