Gavin & Stacey's Alison Steadman broke down in tears when she found out her father had been adopted on ITV's DNA Journey.
The much-loved actress, 76, who plays Pam Shipman in the BBC sitcom, went on the show with her co-star Larry Lamb, 75.
The star was heartbroken to learn her grandmother wasn't biologically related to her and was left reeling from the life-changing news.
As the researchers delved into Alison's DNA history, the actress told Larry she was informed off-camera that her dad had been adopted when he was eight months old.
The star was born in Liverpool to Marjorie and George Percival Steadman, and was the youngest of three sisters.
However, Alison was told there was no genetic link to herself and others that have a connection to the Steadman line after analysing her DNA, which lead back to Isle of Man.
After hearing the shocking news, Alison began to cry as she told Larry: "I haven't' been able to tell you this, but it's been discovered that my father was adopted.
"Nobody knew, no one has ever said a word in the family."
"I really find it hard to believe, he was close to his mother.
"You'd think if he was adopted somewhere along the lines, something would have been said.
"He was a lot younger than his brother and sister and didn't look at all like them, but we didn't think anything of it."
In floods of tears, she continued: "If it is true, I don't know what to say, I just find it quite sad.
"It just means that I'm not related to my grandma."
Recalling the last time she'd seen her father before he died, the much-loved actress said George, who was a production controller had been a wonderful role model.
The Abigail's Party star revealed they had found her real paternal grandmother, May Craine, in the Isle of Man.
Alison also found out she had another aunt, called Margret, who was May's youngest daughter.
Speaking to Larry, she said: "I am still trying to digest the whole thing, it's not easy
"I keep seeing my dad and my grandma, the image of them, and I keep realising how different my dad was."
The star was overcome with emotion as she visited her grandmother's grave, who passed away in 1977, at the age of 89.
"This is not what I thought I would be doing this morning," Alison said.
" It's strange to think my dad's mother is here."
