Viewers have been left stunned by Harry Potter star Warwick Davis’s dark and diverse family history of syphilis and “blacking up” for entertainment.

The actor, 47, appeared on BBC One’s Who Do You Think You Are? on Wednesday night, where he delved into disturbing tales about his ancestry.

The father of four was left both “horrified” and “amused” to find that his great-great-grandfather, Dennis Manning, was a violinist with a travelling troupe who often dressed up as African-Americans to sing songs.

But the most sympathy was generated when he discovered how one great-grandparent died in a mental hospital in Croydon of “general paralysis of the insane”, a disease he later learned was the result of syphilis.

A number of viewers thanked and praised Warwick for sharing the personal stories on national television

The star also took to Twitter himself to comment on his experience.