Veteran actress Julie Walters was left stunned while tracing her family history on U.K. genealogy show Who Do You Think You Are? when she discovered her great-grandfather was once accused of murder.

The Harry Potter star had previously thought of her relative as a hero after finding out he had fought for Irish tenant farmers facing eviction in the 1800s.

However, her impression of him quickly changed when she discovered her great-grandfather Anthony Clarke was charged in 1884 after drunkenly attacking a man with a knife.

The victim later died but it subsequently emerged he had passed away of natural causes and Clarke was convicted of assault.

Walters says on the Bbc show, "I will have to write a script about him. What a life he has had. One minute he is a hero, the next a criminal."

The actress' episode of Who Do You Think You Are? airs in the U.K. on 31 July (14).