Former U.S. secretary of state John Kerry was on the Aga Khan's private island at the same time as Prime Minister Justin Trudeau's ill-fated family vacation last Christmas break, CBC News has learned.

After almost a year of opposition attacks, Trudeau was forced to apologize on Wednesday for the way he handled the trip, after the federal ethics watchdog determined he violated some provisions of the Conflict of Interest Act when he vacationed on Bell Island in the Bahamas and took the Aga Khan's private helicopter to get there.

In her report, Conflict of Interest and Ethics Commissioner Mary Dawson noted that other guests, including someone who she only described as "a senior American official of a previous administration," and friends of those other guests, were also on the island between Dec. 26, 2016 and Jan. 4, 2017.

A spokesperson for Trudeau confirmed Thursday it was Kerry, a one-time Democratic presidential candidate.

A government official, speaking on background, told CBC News Kerry was there at the invitation of the Aga Khan and happened to be there at the same time as Trudeau.

At the time, Kerry still held his cabinet position in the Obama administration. U.S. President Donald Trump won the presidential election in November but didn't take the oath of office until his Jan. 20 inauguration.

While it's not clear what exactly Kerry was doing on the Aga Khan's island, Dawson's report showed Trudeau talked to the Aga Khan about geopolitics, the Muslim world, Canadian leadership on the global stage and problems the Aga Khan was facing.

While recapping the latest trip to the private island, Trudeau said the families exchanged gifts and added that most of the families' interactions happened over meals and were personal in nature.

It wasn't the family's first time on the island. Trudeau had also accepted a vacation for himself and his family in December 2014, and his wife Sophie Grégoire Trudeau set up a trip in March 2016 with a friend of hers and their children.

"The vacations accepted by Mr. Trudeau or his family could reasonably be seen to have been given to influence Mr. Trudeau in his capacity as prime minister," said Dawson's report.

There is an exception in the act for gifts or "other advantages" from friends or relatives, but Dawson ruled it didn't apply because "Trudeau and the Aga Khan cannot be characterized as friends."

Millions in federal aid

Trudeau, whose father struck up a relationship with the spiritual leader of the world's Ismaili Muslims in the 1960s, maintained that he considers the Aga Khan a personal, long-time friend.

Dawson also took Trudeau to task for not recusing himself from two meetings in May 2016 where a $15-million grant to the endowment fund of the Aga Khan's Global Centre for Pluralism was raised.

The Aga Khan is the spiritual leader of millions of Ismaili Muslims and is listed as a member of the board of directors of the Aga Khan Foundation Canada. The foundation, which has received millions of dollars in federal government development aid over the years, is registered to lobby several federal government departments including the Prime Minister's Office, although the Aga Khan is not listed among those registered to lobby on its behalf.

Trudeau meets with the Aga Khan on Parliament Hill in Ottawa on May 17, 2016. Conflict of Interest and Ethics Commissioner Mary Dawson ruled Wednesday that the PM should have recused himself from part of the meeting. (Sean Kilpatrick/Canadian Press)

Trudeau said he regretted not taking proactive precautions to ensure there was no conflict of interest or appearance of conflict of interest.

CBC News has reported Trudeau's trip cost taxpayers more than $215,000 in transportation and staffing costs.

Opposition critics are calling on the prime minister to pay for all, or at the very least, part of those costs.

Conservative MP Peter Kent told The Canadian Press Trudeau owes it to Canadians, given the findings of the Ethics Commissioner. The NDP's Nathan Cullen agreed, saying Trudeau should pick up the tab.

A spokesperson for the Prime Minister's Office told CBC News Trudeau has already reimbursed taxpayers for the commercial cost of flights for him and his family, which is standard practice.

Dawson's office said administrative monetary penalties "are not relevant in this case."

Under the Conflict of Interest Act the commissioner must suspend their investigation and notify authorities if they believe the person they are investigating has committed an offence under an Act of Parliament

In Trudeau's case there "were no reasonable grounds to believe that an offence was committed under an Act of Parliament," said the office.