A tearful Dustin Hoffman has spoken movingly of his Jewish heritage after learning of his great-grandmother’s stint in a Soviet gulag.

The two-time Oscar winner made the harrowing discovery during filming for an episode of US genealogy show Finding Your Roots.

Hoffman, 78, learnt that his ancestor Libba was interned in a Soviet concentration camp after her immediate family were murdered by Bolshevik secret police in the aftermath of Russia’s 1917 revolution.

Already 53 at the time of her imprisonment, Libba survived five gruelling years in the gulag before escaping to Argentina and then finally to America, where she died in 1944 aged 76.

Hoffman’s emotional reaction to his great-grandmother’s story saw him pay tribute to the courage of his Jewish ancestors.

The Rain Man star said: “She was a hero.

“People ask me today: ‘What are you?’ I say, ‘I’m a Jew’. They all survived for me to be here.”

Hoffman, who grew up in a non-religious household, only embraced his Jewish identity late in life – and has spoken of his disappointment at being unable to read Hebrew.

He said in 2006: “I have no one to blame but myself, because I could have learned it. Every one of my kids that has had a bar- or batmitzvah, I’ve had to learn my part phonetically — it’s uncomfortable for me.”