You can't keep a good dog down. K-9 is so popular with children that he quickly returned to Doctor Who following the programme's revival, initially appearing in the episode School Reunion in 2006. The tin dog was rebuilt by the Doctor at the end of that episode, possibly becoming "Mark IV", although the Doctor is careful to confirm that he retains all of his previous memories. When the spin off series, the Sarah Jane Adventures, started, this K-9 was seen locked up in the attic at Bannerman Road to seal a black hole (sentenced to this fate due to the launch of the rival, non-BBC K-9 series). But by the end of the Sarah Jane Adventures' run, K-9 had managed to resolve his contractual difficulties and followed Sarah's adopted son, Luke, to university. Which is where he still is, presumably. Being Luke's roommate hardly seems fair to K-9 so fans can only hope that this "shooty dog thing" ditches his new owner and once again seeks out his true master - the Doctor. Now the rival TV version of K-9 is dead, there are no legal wrangles standing in the way of yet another welcome return for the Doctor's best (metal) friend.