This story has been updated since initial publication with additional statements from Wafic Said. Read more extensive excerpts of his response to CBC News here.

On a cool spring day in 2015, Antigonish, N.S., welcomed two unusual guests: a former prime minister who once called the university town home, and a Syrian-British billionaire known for his sizable donations to higher-learning institutions but also for his role in one of the U.K.'s biggest corruption scandals.

The billionaire, globe-trotting Wafic Said was there to receive an honorary doctorate at St. Francis Xavier University, and the politician, Brian Mulroney, was back at his alma mater as Said's "good friend."

What wasn't known at the time, however, was the true extent of the relationship between the two men.

A joint investigation by Radio-Canada and the Toronto Star, using documents from the Paradise Papers and elsewhere, has found that from 2004 to 2012, Mulroney sat on the board of Said's private holding company based in the tax haven of Bermuda, at the same time as media reports emerged of large-scale corruption in an arms deal that Said helped broker.

A lawyer for Mulroney said the former PM is "proud to have served" on the board of Said's company and considers the billionaire to be "an outstanding man, a highly successful investor and a leading philanthropist."

The investigation also found Said holds a Canadian passport obtained in the early 1990s — and it is not clear how he would have fulfilled the requirement to spend three years in the country to obtain citizenship.

A Panavia Tornado combat plane, one of the types of jets sold to Saudi Arabia as part of the Al-Yamamah arms deal. (Philip Coburn/AFP/Getty) Syrian-born Said made headlines as a middleman who helped broker a colossal 1985 arms deal called Al-Yamamah, where British Aerospace sold billions of dollars in military jets and hardware to Saudi Arabia. "I am proud of the role I played in helping to secure the Al-Yamamah program and with it, many tens of thousands of well-paid and highly skilled jobs in the United Kingdom," he said in an email in response to questions from journalists.

Then years ago, he met Mulroney, and in 2004 invited him to sit on the board of Said Holdings Ltd., a company set up in no-tax Bermuda to manage much of the Said family wealth.

Asked why he chose to sit on the board of a company located in a tax haven, Mulroney had his lawyer answer: "The company is operated with the rigour and governance of a public company…. While Said Holdings may not be subject to tax in Bermuda, it regularly pays substantial sums of tax in other jurisdictions where the company invests."

But Said would face a bigger challenge than tax concerns right around the time Mulroney took up his seat on the board. Investigators were looking into the Al-Yamamah arms deal and unearthing evidence of massive corruption.

At one point, it was reported that a Saudi prince was getting paid $50 million every three months in secret commissions. Other media reports said possibly millions of dollars had moved through Swiss accounts, some of which were held by Said.

But as British fraud investigators homed in on the Swiss accounts, Saudi authorities pressured British prime minister Tony Blair to shut down the probe.

Said himself was never the target of any investigation, nor did he face any charges.

"I was not involved in those cases although I did offer to meet the … investigators to assist them in their inquiries," Said wrote in a statement to CBC. "They did not take up my offer. I was never questioned or charged with any wrongdoing in the U.K. or any other jurisdiction then or subsequently."

Mulroney remained on the board of Said Holdings through 2012.

'I am a Canadian citizen and am proud to be one,' Said wrote in an email. A Paradise Papers record suggests he got the citizenship around 1991, but it is unclear when he lived in the country for the three years needed to meet the residency requirement. (Paradise Papers)

Even as he lived in London and attended meetings in New York, Bermuda and Paris, Said held Canadian citizenship.

One of his passports from 2006 appears in the Paradise Papers. A record filed with it suggests he likely obtained his Canadian citizenship around 1991, which raises the question: When did he live in Canada for the three years needed to meet the residency requirement?

"I am a Canadian citizen and am proud to be one," Said wrote in one of his emails to Radio-Canada and the Star. "At the time I applied for that status, I did not know Mr. Mulroney. Indeed, I did not meet him until several years later, I think in 2002. He had nothing to do with my application....

"I took appropriate professional advice about my entitlement to Canadian residency and citizenship. I followed this advice to the letter, met the relevant qualifications and was granted citizenship."

Canada had an immigrant investor program at the time, under which foreigners pledging to invest $800,000 in the Canadian economy could obtain permanent residency. Said says he was accepted under it in the 1980s.

A spokesperson for billionaire Said said he 'often' used a basement apartment in this Montreal building while he was in Canada.

Said, in a statement to CBC, said he "made what proved to be a very successful investment in Jordan Petroleum, a Canadian oil and gas company. These investments enabled me to qualify for permanent residence and then for Canadian citizenship."

He also incorporated a numbered company around that time, and listed his address on the company's filings as a basement apartment in a down-market Montreal building owned by an immigration lawyer.

Said initially said in an email to Radio-Canada that the small apartment "was rented for me, but when I was there [in Montreal] with my family it was easier to stay in hotels."

Later, a spokesperson for Said insisted in a follow-up email that he definitely lived in Canada for the three years needed to get his residency and "often" spent time in the basement apartment. He also stated he "subsequently purchased a larger apartment" in a more upscale neighbourhood.

I've never seen a billionaire here. — Montrealer Elaine Gloutnez

But shown a picture of Said and his wife, a woman who lived on the third floor of the building from 1987 to 1991 said she had never seen them at the house and had never heard of his name.

"I've been in this area since '85 and I've never seen a billionaire here," Elaine Gloutnez told Radio-Canada.

What's more, corporate filings in Britain show Said was a director of the Bath and Racquets Club in London and listed his "usual residential address" as a building in central London in 1990 and 1991.

Still, Said told the CBC that he "lived in Canada for three years thus complying with the immigration residency requirements" and that he was interviewed by a judge before gaining citizenship.

Veteran immigration lawyer Richard Kurland said the situation "raises a ton of questions."

Said built this luxury country manor in Oxfordshire, England, and also has homes in London, Paris, Marbella, Riyadh and Monaco.

"Was this truly a residence? Was this where the person normally lived? Maybe, but I would have some doubts," he said.

"If this is the apartment, this would be the very first time I see a billionaire living in an accommodation like this."

The head of British NGO Corruption Watch, Andrew Feinstein, who has written a fair deal about Said, added: "I'm not aware of — having pieced together a great deal of his professional history — when he would have spent any meaningful time in Canada."

Back at St. Francis Xavier University in May 2015, it was Said's time to enjoy the spotlight. The university's senate had voted to grant him an honorary doctorate for his philanthropic work. Two months earlier, he'd pledged $4 million toward a new $60-million program at the university: the Mulroney Institute of Government.

"I feel very privileged to have received this honorary degree and to be standing before you in this highly prestigious institution, an institution which has produced many distinguished alumni, including one of the greatest and most successful prime ministers of our time, the Right Honourable Brian Mulroney," he said in his remarks.

The audience applauded. Said, draped in a blue and white academic gown, smiled. So did Mulroney.