The Gavin And Stacey star and co-creator is one of the celebrities taking part in the new series of the hit BBC genealogy show, which sees different famous faces tracing their family history.
During filming, Ruth learned that her paternal grandfather had a pivotal role in the Medical Aid Societies in South Wales, which went on to form the basis of what became the National Health Service.
She said: “I feel so privileged to have been taken on this spectacular journey into my heritage and to have discovered so much about my ancestors.
“I’ve probably been guilty of assuming people from by-gone generations were stuffy, two dimensional and a bit dull. But my trip on Who Do You Think You Are? has proved the opposite to be true.”
More details about Ruth’s family will be revealed when the episode airs as part of the new series, which begins on BBC One next month.
Who Do You Think You Are? has delivered some big bombshells in recent years, but none quite so staggering as EastEnders actor Danny Dyer, who discovered that he is descended from actual royalty.
Meanwhile, Ruth has repeatedly shot down rumours that she and James Corden had been working on a new episode of their hit sitcom Gavin And Stacey, following the success of last year’s Christmas special.
Most recently, she told Jenni Falconer on Smooth Radio: “We wouldn’t want to come up with something that was substandard. The last thing we want to do is disappoint.”
This article originally appeared on HuffPost UK and has been updated.