Harry's grandfather (Knock Knock)

Harry had a grandfather.

In 2017, Harry mentioned that his granddad 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 that Harry's grandfather was the Fourth Doctor's companion Harry Sullivan. This dialogue was cut ahead of transmission.