Harry's grandfather (Knock Knock)

In 2017, Harry mentioned that his grandfather and his grandfather's boyfriend were arrested in China after attempting to steal a section of the Great Wall of China. (TV: Knock Knock)

Behind the scenes
Prior to transmission of Knock Knock, it was stated on the official Doctor Who website and in an interview with Mike Bartlett that Harry's grandfather was the Fourth Doctor's companion Harry Sullivan. This dialogue was cut ahead of transmission. (DWM 512)