The 47-year-old host of The X Factor revealed he had been approached about appearing in the BBC documentary series, which sees celebrities trace their family tree – but researchers told him they hadn't found anything of interest in his past.
O'Leary told parenting podcast Sweat, Snot And Tears: "They actually researched my family for about three months. They came back and said: 'There's just not enough interesting stuff about your family.'"
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The TV presenter – who welcomed his first child with wife Dee Koppang in June 2020 – was born in Essex, but holds both British and Irish citizenship as his parents are Irish. O'Leary claimed the researchers had not tried hard enough to unearth the truth about his ancestors.
He went on: "Wexford is a port town, and my family are all seafaring folk. I have it on good authority that two of them went to America.
"One of them was a police officer and the other was a judge and they both got killed by the Mafia in the 30s.
"They couldn't find any record of this. I was like, 'What are you on about? We've been everywhere, we're a family of sailors.'
"I just don't think they were trying hard enough. It's awful, isn't it? Absolutely awful."
But O'Leary need not be too offended, as he is not the first celebrity to be told their family history was too dull for the show.
Other famous faces who have admitted to being approached by Who Do You Think You Are? only to be told they hadn't made the grade include TV presenter Sir Michael Parkinson.
The 85-year-old told the Radio Times in 2009: "When Who Do You Think You Are? called and asked if I was interested, I said I would be delighted, but warned that my own research had unearthed nothing of note.
"'Oh, they all say that. But we always find something,' they said. Six weeks later they phoned to apologise. My story was so boring they had to cancel the entire project. I was gutted."
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