Justin Trudeau apologises for wearing brownface makeup to a party 18 years ago.

Highlights TIME magazine published 2001 photo of Trudeau in brownface make-up

Canadian Prime Minister admitted to wearing blackface in high school

He had kicked off campaign for re-election last week

Canadian Prime Minister Justin Trudeau apologized Wednesday for wearing brownface and blackface after a yearbook picture surfaced showing him at an Arabian Nights-themed party in 2001, embroiling the politician in another scandal as he faces a tough battle for a second term.

The photograph, published Wednesday by Time and taken while Trudeau was a teacher at the private West Point Grey Academy in Vancouver, depicts the then-29 year-old smiling while wearing a feathered turban, his face darkened in a practice with racist roots.

"I attended an end-of-year gala where the theme was Arabian nights. I dressed up in an Aladdin costume and put makeup on," Trudeau said at a news conference Wednesday evening. "I shouldn't have done that. I should have known better, but I didn't, and I'm really sorry."

Trudeau also admitted to wearing blackface in high school while singing the song "Day-O" at a talent show.

The prime minister kicked off his reelection bid last week amid a political climate that has grown increasingly grim for the Liberal Party leader once considered an international darling. Trudeau faces a formidable challenge from Conservative Party leader Andrew Scheer, who blasted his opponent Wednesday night, calling the brownface photo "an act of open mockery and racism."

Speaking to reporters in Sherbrooke, Quebec, Scheer said he was "shocked" and "disappointed."

The Conservatives, who are in a dead heat with the Liberals, have accused Trudeau of being "not as advertised."

Trudeau, who said in his apology Wednesday that he has "worked all [his] life to try and create opportunities for people to fight against racism and intolerance," has positioned himself as a champion of diversity and inclusiveness. He earned international acclaim in 2015 when, as the new prime minister, he unveiled a diverse, gender-based cabinet - "a cabinet that looks like Canada," as he put it then. He has boasted about having more Sikhs in his cabinet than Prime Minister Narendra Modi does in India.

Speaking from a campaign plane in Halifax, Trudeau said that he now recognizes brownface as "racist."

He added that he spent the evening calling friends and colleagues and has "many more calls to make."

The story landed like a bomb one week into a campaign that has seen the Liberals digging up and releasing old social media posts and videos from Conservative candidates that they say show that the party is welcoming to those who hold insensitive and intolerant views.

Earlier, Scheer said that he would support candidates who made mistakes in the past, provided that they apologize, recognize their errors and take responsibility for their actions.

"I accept that people can make mistakes in the past and can own up to that and accept that," Scheer told reporters earlier this week. The Conservatives, who are in a dead heat with the Liberals, have accused Trudeau of being "not as advertised."

The National Council of Canadian Muslims thanked Trudeau Wednesday evening for his swift apology, after tweeting a statement from Executive Director Mustafa Farooq calling the prime minister's use of brownface "deeply saddening."

"The wearing of blackface/brownface is reprehensible, and hearkens back to a history of racism and an Orientalist mythology which is unacceptable," Farooq's statement read.

Jagmeet Singh, a turban-wearing Sikh who leads Canada's left-leaning New Democratic Party, called the photograph "troubling" and "insulting." At a news conference in Mississauga, Ontario, he spoke directly to those who have experienced racism and "might feel like giving up on Canada. I want you to know that you have value, you have worth and you are loved," he said, his voice breaking.

Green Party leader Elizabeth May also shared her dismay.

"I am deeply shocked by the racism shown in the photograph of Justin Trudeau," she tweeted. "He must apologize for the harm done and commit to learning and appreciating the requirement to model social justice leadership at all levels of government. In this matter he has failed."

Trudeau has been panned before for his attire choices. Last February, he faced scrutiny for wearing embroidered kurtas and sherwanis - traditional Indian garb - during a diplomatically awkward trip to India. In response to criticism over his many costume changes on that sojourn, he told reporters: "I have long been known to wear traditional clothes to a broad range of events in many different communities in Canada and elsewhere."

Trudeau is also battling a furor over alleged ethics violations after the country's attorney general accused government officials of pressuring her into reaching an out-of-court settlement with an engineering firm from Trudeau's home province that was charged with bribery and corruption.

In nationally televised parliamentary hearings, the attorney general, Jody Wilson-Raybould, said she received "veiled threats" and was demoted when she refused to succumb to the pressure.

The allegations set off a political firestorm and triggered several high-profile resignations, including Wilson-Raybould's, who was then expelled from the Liberal Party. Trudeau - who pitched Canadians on running a transparent government that would be open to diverse views - stood accused of shady backroom dealings and judicial interference, of being a fake feminist, and of bullying Wilson-Raybould, an indigenous woman.

South of the 49th parallel, white American politicians have a lengthy history of racist pantomime. U.S. lawmakers from both parties have faced scrutiny and scorn for wearing blackface - a caricature of black people inspired by minstrel shows dating back to the 1830s.

Most recently, Alabama Gov. Kay Ivey, a Republican, apologized last month for wearing "some black paint all over her face" during a college skit in 1967. And earlier this year, Virginia Gov. Ralph Northam, a Democrat, admitted to wearing blackface to impersonate Michael Jackson.

The Northam incident began a national outcry that shed new light on the racist past of Northam and the scores of other politicians who for years have emerged from similar scandals relatively unscathed.