Prime Minister Justin Trudeau brought along a fellow MP and the Liberal Party president on his family vacation in the Bahamas to the private island property of billionaire spiritual leader, the Aga Khan.

The PMO confirmed that Liberal MP Seamus O'Regan and his husband Steve Doussis, as well as Liberal Party President Anna Gainey and her husband Tom Pitfield, were guests on the family trip. The story and new details were first reported by The National Post.

PMO spokesman Cameron Ahmad told CBC News that no other MPs or designated public office holders were on the trip, and that none travelled on Challenger government planes.

"As the prime minister said yesterday, we are of course happy to answer any questions the [ethics] Commissioner may have. Beyond that, we are not in a position to comment further," he said.

O'Regan, a former television host and long-time friend of Trudeau's, said he flew on his own and did not travel with the prime minister.

"It was personal time, private time. When I returned to Canada I went to the commissioner's office and voluntarily disclosed the trip," he told CBC.

He said he reported the trip to the commissioner's office on Jan. 8, days after he returned home and after media reports on Trudeau's trip. O'Regan declined to comment on how he or the prime minister made their way to Bell Island, and said he travelled from there on to Cuba for an extended vacation.

'It's inappropriate'

NDP ethics critic Alexandre Boulerice said he initially took Trudeau's explanation at his word — that it was a family vacation. But he said the latest developments suggest it was something much different and it "doesn't look good."

"It's less and less a private meeting with a friend of the family and more like a lobbyist trying to get something from the Trudeau government," he said. "And it's inappropriate."

Today, Conservative ethics critic Blaine Calkins sent a letter calling for an investigation into the transportation and hospitality extended on the trip. If Trudeau's relationship is so close with the Aga Khan that he is deemed a "friend" under the rules, then the prime minister was obliged to have an ethics screen and recuse himself from any discussions involving the Aga Khan's foundation, his letter argues.

Calls for ethics investigation

"In light of the many unanswered questions and the serious concerns that they raise, I think it is important that you open a full investigation," Calkins says.

Earlier this week, Ethics Commissioner Mary Dawson's office said it was considering an investigation into Trudeau's holiday after receiving a complaint from Conservative leadership candidate Andrew Scheer.

The Saskatchewan MP wrote a letter Monday asking Dawson to rule on whether Trudeau's stay on the Aga Khan's private island is a gift that violates the Conflict of Interest Act.

Prince Karim Aga Khan IV is the hereditary spiritual leader of the world's 15 million Shia Ismaili Muslims and a multimillionaire philanthropist.

Government funds foundation

The federal government has contributed millions to the Aga Khan Foundation to help fund its international development projects. The most recent grant was a five-year, $55-million project to improve health services in Afghanistan that was announced in December 2015 under the Trudeau government.

Scheer pointed to Section 14.1 of the act which stipulates an MP should not accept "directly or indirectly, any gift or other benefit ... that might reasonably be seen to have been given to influence the [MP] in the exercise of a duty or function of his or her office."

Asked about the trip Tuesday, Trudeau insisted it was a private trip and that the Agha Khan is a long-time family friend who served as a pallbearer at his own father's funeral.

"This was our family vacation, and I will answer any other questions that the ethics commissioner has for me," he said. "And I'm sure we will have more discussion about this in the coming weeks."

According to the Open and Accountable Government guide Trudeau brought in shortly after taking office, ministers and parliamentary secretaries must not accept sponsored travel on chartered or private aircraft except in exceptional circumstances, and "only with the prior approval of the Conflict of Interest and Ethics Commissioner. "