ROBERT DE NIRO was on a mission to find the long-lost relatives who had helped turn the star of The Irishman into a true Irishman.

Despite his name, the well-known actor Robert De Niro is more Irish than Italian. His father, Robert Sr., was half-Irish from his mother Helen O’Reilly’s side of the family, who are completely Irish, and three of his four grandparents had Irish origin.

The 76-year-old Oscar winner has asserted that he is an authentic Irishman while promoting the new picture, directed by Martin Scorsese.

He also wants to track down long-lost ancestors on this side of the Atlantic.

He describes how, as a youngster in the 1960s, he toured across Ireland. His father, Robert Sr., was half-Irish, and his mother, Helen O’Reilly, came from an Irish family.

He’s said: “Yeah, I have Irish roots. My mother’s Dutch, French and German. And my father was Irish and Italian.

“I hitchhiked around Ireland when I was about 18, 19.

“I’ve been trying for years to find relatives there.

“For some reason, it’s not easy. Italy was easier.”

In 1962, he walked from Dublin to Galway and then boarded a boat to the Aran Islands before continuing south on the continent.

De Niro said: “People gave me blankets for sleeping outside and I had breakfast with them in the morning. They were very friendly.”

He’d struggled to find any true distant surviving relatives who could assist him fill in the blanks on his family’s long-lost existence in Ireland until he saw the movie.

De Niro has been looking for answers to this predicament but has so far been unsuccessful.

For years afterward, there were rumors that De Niro was seeking for a vacation property near Cushendall, a rumor that the BBC’s One Show revived two years ago while on a road trip across Northern Ireland.

Martin Scorsese’s film is based on Charles Brandt’s non-fiction book “I Heard You Paint Houses” which was published in 2004 and tells the true story of Irish American criminal Frank Sheeran, a Mafia hitman who worked for crime lord Russell Bufalino and labor leader Jimmy Hoffa.

“I heard you paint houses,” the title of the book, was a code phrase used over the phone to employ Sheeran to kill someone.

De Niro said: “I read it and said, ‘Jesus. To me this story’s kind of great.

“It was fascinating and simple. I liked the character: how he was introduced to this world and slowly saw how it worked.”

Shortly after De Niro’s interviews appeared in American media, Kate and Mike Lancor of New Hampshire, two Irish genealogy specialists, claimed to have found answers for him after using De Niro’s father Robert senior as a starting point.

From his mother Helen O’Reilly’s side of the family, the actor’s grandfather was half Irish, and the Lancors were able to trace her ancestry down to Co Tipperary.

During the Irish famine of 1840, the O’Reilly family immigrated to America, and the actor’s grandmother married his grandpa Henry De Niro when she was 21 years old.