From Here To Paternity (S21E07)

Compo gets an unexpected letter after many years. Curious, Clegg and Truly decide to open it, only to uncover Compo's long-held secret: he has a son. The letter is from Tom, who reaches out in hopes of reconnecting with his father after their long estrangement. When Tom finally arrives in town, Compo and his friends face the challenge of revealing the surprising truth to him.