Former British Prime Minister Boris Johnson reportedly claims in his new memoir "Unleashed" that US President Joe Biden privately told him that he's "not really Irish."

Johnson, who was Prime Minister from July 2019 through September 2022, wrote of his and Biden's engagements surrounding Brexit in his newly released memoir.

According to The Irish Times, Johnson wrote: “In fact, he [Biden] disarmed me completely by saying that his family origins were not really Irish at all, and that the Bidens were an old seafaring family from Kent (which seems plausible, since -den is a common Kentish termination).

“I suppose he may say something else when in Dublin. But never mind!”

Indeed, research has found that Biden's great-great-great grandfather William Biden was from Westbourne in West Sussex, England, and later emigrated to Maryland in the US.

While he has a British link, Biden's Irish roots are more apparent. All eight of his great-great-grandparents on his mother's side were born in Ireland, as were two of his great-great-grandparents on his father's side.

Biden has earned a reputation for his embrace of his Irish roots.

In a 1987 interview with IrishCentral's sister publication Irish America Magazine, then-Senator Biden said: "I always thought of myself as Irish. I never called myself anything else. I was Irish to the point that my dad used to get angry at times. He’d say, 'Your mother’s a Robinette, you’re part French.' I always used to say, 'No, I’m Irish.'"

In the same interview, Biden recalled how his grandmother would tell him: "Remember, Joey Biden, the best drop of blood in you is Irish.”

Throughout his lengthy political career, Biden has often taken an assist from Irish writers including Seamus Heaney and James Joyce in his speeches. Most recently, he quoted WB Yeats at his final UN General Assembly address.

Biden has also made his Irish roots a bit of a punchline a number of times, often drawing mixed reactions.

In 2020, the President-elect went viral when he cheekily replied to a BBC reporter saying: "The BBC? I'm Irish."

The moment when @NickBryantNY asked @JoeBiden for a quick word.

He replied with a smile, “The BBC? I’m Irish.” #PresidentElect #Election2020 pic.twitter.com/gjsLCxmlLq

— Darran Marshall (@DarranMarshall) November 7, 2020

Last year, the President said he made his much-hyped visit to Ireland "to make sure they weren't - the Brits didn't screw around."

He has on several occasions said "I may be Irish, but I'm not stupid," and, in 2021, he told Pope Francis, “I'm the only Irish man you've ever met who's never had a drink."

Johnson's claim that Biden told him he's "not really Irish" is notable considering Peter Westmacott, the former UK Ambassador to the US, has written: "Johnson has never wanted to accept that Biden is an Irish-American Catholic who cares deeply about the island of Ireland."

The Irish Times further reports that Johnson claimed Biden, in the scope of Brexit, "defied the urgings of the European Union and, I believe, of some of his own officials - and pointedly refused to weigh in on the [Brexit border] row over Northern Ireland."

This claim comes in contrast with Biden's vocal defense of the Good Friday Agreement during Brexit. In a post in September 2020, before he was elected President of the United States, Biden wrote: “We can’t allow the Good Friday Agreement that brought peace to Northern Ireland to become a casualty of Brexit."

We can’t allow the Good Friday Agreement that brought peace to Northern Ireland to become a casualty of Brexit.

Any trade deal between the U.S. and U.K. must be contingent upon respect for the Agreement and preventing the return of a hard border. Period. https://t.co/Ecu9jPrcHL

— Joe Biden (@JoeBiden) September 16, 2020