Monarch of the Glen (2000)

S1E4 Episode 4

Hector's friend, a genealogist, uncovers a diary revealing that Katrina's mother, who once worked as a servant in the household, had an affair with someone identified as ‘H.’ This revelation understandably disturbs Molly, who is troubled by what it suggests. However, the situation takes a surprising turn when they learn that the elusive ‘H’ is none other than the genealogist himself, Katrina's father.