American actress Mandy Moore took part in the US version of Who Do You Think You Are and discovered that one of her ancestors died in a workhouse in Ireland during the famine.

The This Is Us star travelled to Cashel, Co Tipperary where she learned that her four times great grandmother, Mary Flynn, died aged 40 at a workhouse.

The 34-year-old actress was reduced to tears when she learned of her ancestor's tragic death.

Historian and author Turtle Bunbury travelled with Moore to Cashel, where he revealed the sad news about Mary Flynn's life and death at a workhouse, which is now a hospital.

He took Moore to visit Donaghmore Workhouse, which is located nearby and is now a museum, and told her that Mary and her two daughters spent time living in terrible conditions as the famine ravaged the country.

"They were hell on earth.  This was the last resort," he said of the workhouses.

"They were death traps," he added.

Moore said: "To know that my four times great grandmother passed away in a place like this and the horrific conditions you described, is really... it's just very tragic."

The actress was told that her great, great, great great grandmother would not have had a wake or a funeral, or a marker on her grave, which caused her to become emotional.

"That's heavy to think about, you know.  I didn't even know her name until just a few days ago and to think that no one has thought about or remembered her until now for all these years... it's a lot."

"I'm honoured and humbled that I could be a representative of the family to just tell her that she's not forgotten," Moore said. "I can feel her. I can feel the energy of everybody that's here, but definitely I can feel her."

Moore also discovered that Mary's daughter Ellen fled the workhouse when she was just 15. She travelled for four months on the Lady Peel ship with her older sister Mary to work as a domestic labourer in Australia.  The actor also found out that Mary had died before Ellen set sail. 

"It sounds like her life was so perilous in Ireland that this was by far a better option than staying home," she said. "It makes so much more sense now."

Moore visited the immigration hall in Australia where Ellen would have arrived after the four month journey. She described Ellen as a "survivor", saying: "I wouldn't be here, I would not exist, had it not been for the way in which Ellen led her life."