“When my grandfather disappeared, nobody had any idea where he had gone,” Mike O’Connell tells the Irish Examiner.

“But for a short time, he sent money, small amounts. On the envelope it said Santander, Spain, and that was the only clue.

“My granny, his wife, and others in the family spent their whole lives waiting for the return of this beloved father.

"They were in the dark completely. When I got to about 15, it occurred to me how can he be such a beloved creature when he clears off, disappears, deserts them, and leaves them in poverty? Years later, when Sue took it up, her only clues were football and Santander, and that’s where she started.”

Mike is Patrick O’Connell’s grandson, and his wife Sue is the author of The Man Who Saved FC Barcelona: The Remarkable Life of Patrick O’Connell.

Recreating the life of one of Irish sport’s most remarkable and significant figures, it is published this month in Ireland and England by Amberley Books, and has its origins in a happier love story.

“Mike and I met in Madrid,” Sue says.

“We were both working at an English language school and used to get the school bus together. Basically, he was chatting me up, and I didn’t realise it. One of the stories he told me was about his grandfather.”

The ploy worked pretty well, and the couple returned to England together.

However, Sue could not leave Mike’s grandfather behind. Over 15 years she gradually uncovered the almost incredible story of the centre-half who captained Ireland to the 1913/14 British Home Championship, was sacked by Manchester United for match-fixing, managed Real Betis to their only La Liga title and — famously — saved FC Barcelona during the Spanish Civil War. Based on family recollections collected by Sue, and researched in England, Dublin, Belfast, Spain, Mexico and New York, The Man Who Saved FC Barcelona is not really about football.

It’s more focused on the man who moved to Spain without telling his family anything, and the wife and four young kids left behind to struggle in the dark.

It is told in many fragments in different voices through recreations of Patrick’s own letters, correspondence from his two wives, contemporary newspaper articles, his young daughter Nell’s heart-wrenching diary entries, and his son Dan’s coming-of-age story.

Throughout his life, O’Connell shows a Forrest Gump-style ability to be on the spot as history unfolds.

The book says he ran guns during the 1916 Easter Rising as a favour to his former Belfast Celtic team-mate Oscar Traynor. His son Patrick Jr was a child in the crowd at Croke Park on Bloody Sunday in 1920.

He talks politics with Barcelona president Josep Sunyol, just before the Catalan nationalist is murdered by Francoists in 1936. He also, of course, rescues Barcelona by leading them on tour to Mexico and New York in 1937.

“Opportunities occurred and he took them,” says Sue.

“Something happened and it was good, it was interesting, so he did it. Generally, he was very good at everything he did. At Boland’s Mills, very young, he was already a foreman. Then, his football career started and he went from success to success. What higher level can you get than captaining your country?

"He even tried his hand at bullfighting. He was spectacularly bad at it, but he tried it. He was brave. And he’d try anything, I think. If there was an opportunity, he took it.”

In those pre-mass-media days, none of the family left behind knew of Don Patricio’s successful career until Dan did some solo detective work in a Dublin pub following a 2-2 draw between Ireland and Spain at Dalymount Park in November 1955.

“After the match, Dan spoke to some of the Spain players about a relative of his with the name of O’Connell,” says Mike.

“He found out his father was in Seville. [He travelled over] and they met daily in a park for a week. They didn’t get on. Dan had to pretend he was a nephew, as his father had married again and nobody [in Spain] knew he had a family in England.”

In another exceptional twist the two wives were quite similar, if with an age gap of over 20 years. O’Connell’s first wife Ellen [nee Treston] had come from a bohemian middle-class Dublin family, and was swept off her feet by the dashing young footballer.

His second wife, Ellen [nee O’Callaghan] was working as a nanny for British diplomats in Spain when she fell for the much- respected middle-aged manager. Neither woman knew the other existed.

“Ten years ago, the second Ellen’s great-nephew managed to get in contact and told me about the second marriage and Patrick’s bigamous life,” Sue says.

“We always knew he was a man for the ladies, but this was quite astounding. She actually looked like his first wife. She was Irish. And she had the same first name. I couldn’t believe it. I think he genuinely loved her, and in those days you couldn’t just move in with your girlfriend, so he had to marry her. I don’t think she had any knowledge of what he had done before until near the end.”

By the end, O’Connell had moved to London, where he died in poverty in 1959. His life and career were gradually forgotten by almost everyone until Sue’s painstaking work brought him back into the spotlight, inspiring the founding of the Patrick O’Connell Memorial Fund, and a series of newspaper articles and TV and radio documentaries. His grave in London has been restored.

A memorial plaque now sits on the wall of the house on Fitzroy Avenue in Dublin where he lived as a boy. O’Connell features in a mural on Belfast’s Falls Road. And the FAI’s Abbotstown HQ has a ‘commemorative alcove’ filled with memorabilia.

Mike and Sue’s journey has seen them meet people and visit places they would never have expected. The new book has forewords by Martin Buchan, who was also a Manchester United captain, and Maureen O’Sullivan, TD for Dublin Central, where O’Connell was born in 1887.

The pair have also met high-profile figures, from Sinn Fein leader Gerry Adams to Barca’s current club president Josep Maria Bartomeu, who welcomed the couple to the Camp Nou last December.

The O’Connells also then met the family of Angel Mur, who travelled with Barca to America in 1937 after being promoted unexpectedly from groundsman to team physio.

“Patrick wanted to take Angel Mur with him, but you couldn’t take groundsmen on tours,” says Mike.

“So he made him the physio, and taught him the basics on the boat over. From that day onwards the Mur family have always been Barca physios. His grandson is now at the club, and his daughter is a physio too and it all went back to Patrick. The two grandsons met earlier this year at the Camp Nou. It was very emotional. It’s typical Barcelona for you.”

Such unlikely tales are scattered throughout The Man Who Saved FC Barcelona: The Remarkable Life of Patrick O’Connell, published exactly 80 years after that salvation was achieved.

The book presents a man who, despite his clear personal failings, inspired quite amazing affection, even in those who might be expected to think otherwise.

“Mike always says that I married him, but I fell in love with his granddad,” says Sue. “It is such an interesting story. I’ve not come across anybody who has not been fascinated by this story.”

Barca are in Dublin facing Glasgow Celtic at the Aviva Stadium as part of the International Champions Cup summer friendly programme.

Barca are expected to field first-team stars, including Lionel Messi, Luis Suarez, and summer signing Denis Suarez, as Luis Enrique’s team step up their preparations for the 2016/17 La Liga season.

This morning, the Patrick O’Connell Memorial Fund’s Fergus Dowd and Alan McLean have organised an event at Dublin City Council’s offices on Pearse Street to mark Barca’s visit to Ireland, and the publication of The Man Who Saved FC Barcelona: The Remarkable Life of Patrick O’Connell.

Aside from Sue and her husband Mike, other invitees include Spain’s ambassador to Ireland Jose Maria Rodriguez Coso, Lord Mayor of Dublin Brendan Carr, TD for Dublin Central Maureen O’Sullivan, and a contingent of senior Barcelona representatives.