When news of Justin Trudeau’s holiday visit to a private Caribbean island leaked out, the prime minister’s political opponents were quick to label the vacation a conflict of interest.

That’s because the Aga Khan, the island’s owner and a respected religious leader who presides over a network of charities, also runs a foundation that receives millions from the Canadian government.

The prime minister defended the trip this week, saying it was a private visit with an old family friend, which he argues is in line with conflict-of-interest codes.

Here’s what you need to know about the controversy, starting with the basics:

Who is the Aga Khan, anyway?

Prince Shah Karim Al Hussaini, Aga Khan IV, is the spiritual leader of the world’s 15 million Ismailis, who follow a branch of Shia Islam. He is also a philanthropist who runs one of the world largest private charities — the Aga Khan Development Network.

The Aga Khan, 80, is also extremely wealthy.

Forbes magazine listed him as among the world’s 10 richest royals in 2010, with a fortune of $800 million. He owns and operates one of France’s largest horse racing and breeding operations, as well as many other businesses, including luxury hotels.

His wealth stems in part from the fact that Ismailis are obliged to tithe, giving a percentage of their earnings to the Aga Khan, which he in turn invests in his charity network.

In his private life, the Aga Khan is twice divorced, with three children with his first wife, a former British model, and one with his second, a German-born former pop singer.

And who are Ismailis?

Ismailis are a minority within a minority in the Muslim world.

Most of the world’s 1.3 billion Muslims are Sunni, not Shia, dating back to the 7th-century schism that followed the death of the prophet Muhammad. The Ismaili sect then broke with the Shia minority in the 8th century over further disagreement about which of the prophet’s descendents should lead.

An Ismaili dynasty controlled a large area of North Africa and Egypt for a period stretching into the 12th century, before declining. Followers of the sect have been without a homeland, since, and have often been persecuted.

Today most Ismailis accept that the Aga Khan is their 49th Imam and a direct descendant of Muhammad.

What does the Aga Khan Development Network do?

In 2013, Vanity Fair described the Aga Khan’s global charity network as a “staggeringly large and effective organization,” akin to “his own UN … that also includes an enormous portfolio of for-profit businesses.”

The network employs 80,000 people in 30 countries, operating universities, hospitals and school programs for people in poor and war-torn parts of the world, regardless of their faith.

The Aga Khan’s Canadian charity, the Aga Khan Foundation, is part of this network. Since 2004, the Canadian government has sponsored 16 global development initiatives in partnership with the foundation, worth a total of more than $300 million.

The foundation’s projects do everything from supporting craft producers in Mozambique to investing in childhood education in Bangladesh or working to improve women’s health in Afghanistan.

So, what’s so bad about the prime minister visiting the Aga Khan’s private island?

Potentially nothing, but a helicopter ride during the vist may have broken the law.

Trudeau admitted Thursday that he travelled on the Aga Khan’s private helicopter, which may have broken federal law — the Conflict of Interest Act says that Trudeau can’t take a private aircraft without permission from the ethics commissioner, Mary Dawson.

A spokesperson for Dawson declined to confirm whether Trudeau had sought permission for the ride.

Also on Thursday, the commissioner’s officer confirmed it had started a “preliminary review” of the trip.

Earlier this week Andrew Scheer, an opposition MP and Conservative leadership candidate, asked Dawson to investigate if the visit was a conflict of interest, the problem being that the Aga Khan is chairman and director of the foundation, which is a registered federal lobbyist.

Federal conflict-of-interest laws allow the prime minister to take gifts from friends or relatives, but not from lobbyists; which category the Aga Khan falls under appears to be up for interpretation.

“The Aga Khan has been a long-time family friend,” Trudeau said this week. “As for the conflict of interest commissioner, the ethics commissioner, I look forward to answering any questions she may have.”

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This week, the Prime Minister’s Office confirmed that Newfoundland MP Seamus O’Regan and his husband, as well as Liberal party president Anna Gainey and her husband were also guests of the Aga Khan over the holidays.

The Aga Khan has not commented on the controversy; neither has the Aga Khan Foundation in Ottawa.

What is the Aga Khan’s relationship with the prime minister and with Canada?

The Aga Khan’s relationship with the Trudeaus goes back to the 1970s when Ugandan dictator Idi Amin expelled Ismailis from his country. The Aga Khan called on then-Prime Minister Pierre Trudeau to give his people a safe haven, and Canada took in 7,000 Ismailis.

“He was a pallbearer for my father’s funeral. He has known me since I was a toddler,” the prime minister said of the Aga Khan’s relationship with his family.

Today, an estimated 100,000 Ismailis live in Canada, and the Aga Khan enjoys ties to many of Ottawa’s political elites.

In 2008, the Aga Khan opened a de facto embassy to Canada in Ottawa.

For his ties to Canada and his reputation as a philanthropist, the Aga Khan has received praise from both Liberals and Conservatives: In 2009, he was named an honorary Canadian by then-Prime Minister Stephen Harper.

Last September, the Aga Khan received the inaugural Adrienne Clarkson Award for Global Citizenship.

“I believe Canada is one of the greatest countries of opportunity,” he said in his acceptance speech in Toronto. “Canada welcomes newcomers and helps them integrate. That’s not true of many western European countries.”

Does the Aga Khan have any connections to Toronto?

Yes. Toronto’s Aga Khan Museum opened in 2014 to promote knowledge of Islamic culture and art.

The 10,000 square-metre museum, designed by architect Fumihiko Maki, is set among formal gardens near Eglinton Ave. and Don Mills Rd. Its current special exhibit, Syria: A Living History, features artifacts from the war-torn country. Syrian refugees and their sponsors are invited to come for free.

So, how did the Aga Khan become the Aga Khan?

The short answer is he was born into the job: The young Aga Khan succeeded his grandfather, Sultan Mahomed Shah, Aga Khan III, in 1957. At the time he was 20, studying Islamic history at Harvard.

In his will, the elder Aga Khan wrote: “I am convinced that it is in the best interests of the Shia Muslim Ismailia Community that I should be succeeded by a young man who has been brought up in the midst of the new age and who brings a new outlook on life.”

At the time, the Aga Khan’s father, Prince Aly Khan, had a reputation as a jet-setter — he divorced the current Aga Khan’s mother to marry Hollywood star Rita Hayworth in 1949.

It was the first time that a generation had been passed over in the sect’s 1,300-year history, the New York Times reported at the time.

With files from The Canadian Press and Alex Ballingall

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