The comedian and Great British Bake Off host features in a forthcoming episode of the BBC One genealogy programme where he investigates his Jewish family's experiences in Europe during World War II.
Lucas is amazed to find that one of his relatives was living as a lodger with the Frank family and spent their last night at home with them before they went into hiding, even being named in Anne Frank's diary.
Little Britain star Lucas travels to Amsterdam in the programme, where he is told more about his grandmother Margot's cousin Werner Goldschmidt.
As he is shown a card of Goldschmidt's details, including his address when he first moved to Amsterdam, he notices the name "O. Frank" listed as his landlord and asks a historian: "That's not Otto Frank, is it?"
The historian replies: "It is," and Lucas clarifies: "What, Anne Frank's father?"
He says, "Exactly," and goes on to explain that Goldschmidt was lodging in an apartment with Otto Frank, his wife and two daughters — one of whom was Anne — after moving to the city as a divorced man in his 30s.
Lucas says: "So my ancestor would have known Anne Frank, the writer of one of the most important books ever written.
"It's the one story everyone knows, if you know no other story about what happened to the Jews in World War II you know the story of the Frank family."
But when Lucas goes to see the apartment that they shared, he finds out something even more remarkable about his ancestor, that he is named in Anne Frank's diary.
Writing about the night before her family left their apartment to go into hiding in the attic of another house and the preparations they made, she told how their lodger Goldschmidt stayed up talking to the family until 10pm that night, despite their polite hints that he should go to bed.
However, Goldschmidt had no idea that his landlords were planning their escape.
Lucas said: "I would have read this diary when I was younger and never realised that she was talking about a relative of mine."
Matt Lucas' episode of Who Do You Think You Are? airs on Thursday, 16 June at 9pm on BBC One.
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