Thicker than Water

"Thicker than Water" is the third Christmas special episode of the BBC sitcom, Only Fools and Horses, broadcast on 25 December 1983, and is the first to be screened on Christmas Day. Synopsis Rodney and Grandad are watching television on Christmas Day, when a stranger appears at the door. The stranger turns out to be Del Boy and Rodney's father (and Grandad's son) Reg, who had abandoned them 18 years earlier after the death of their mother. When Del learns of Reg's return he intends to eject him, but Rodney and Grandad persuade Del to give him a chance. Reg tells his family that he has been living in Newcastle and has recently been diagnosed with a hereditary blood disorder. Del and Rodney quickly take blood tests, which both turn out negative when they receive their results on New Year's Eve, but Grandad notices on their results that they have different blood types. Grandad explains that around the time that Rodney was born, Reg and their mother Joan were having frequent arguments, and Joan flirted with other men. Del and Grandad thus both assume that Rodney has a different father and tell him the news, with Del concluding that Rodney is a "whodunnit". However, when Reg returns having checked his own and Grandad's blood groups, he reveals that it is in fact Del who has the alien blood group. The next day, New Year's Day, Del is drinking alone at The Nag's Head while Reg moves in permanently, wearing Del's clothes, spending time with Rodney and taunting Del for being a "lone ranger".