Canadian Prime Minister Justin Trudeau apologized on Wednesday after a photo was published of him in 2001 wearing make-up to darken his skin at an Arabic-themed party – a practice called blackface’.

“Blackface” is considered offensive because it refers to a 19th century theatrical custom, considered racist, where white actors would color themselves with charcoal to portray black characters on stage, often in a cartoonish way.

Time magazine published the photo, included in the yearbook of West Point Gray Academy, a private school in British Columbia, where Trudeau worked as a teacher before entering politics. It shows Trudeau wearing a turban and tunic as a costume, with dark makeup on his hands, face and neck.

According to the Associated Press, Trudeau, who launched his re-election campaign exactly a week ago, said he should have known better how to behave.

“I’m mad at myself, I’m disappointed in myself,” Trudeau told reporters traveling with him on his campaign plane.

Canada’s prime minister is just the latest politician to come under fire for racially insensitive photos and actions among young people. Earlier this year, Virginia Governor Ralph Northam came under intense pressure to resign after a racist photo appeared on the page of his 1984 medical school yearbook. He denied to be in the picture but admitted to wearing “black face” as a youth, while portraying Michael Jackson at a dance. party in the 1980s.

Trudeau said the photo was taken at the school’s annual dinner, which was themed “Arabian Nights” that year. The Prime Minister would be dressed as a character from “Aladdin”.

He said it was not the first time he wore makeup, saying he did the same when he performed Harry Belafonte’s song “Banana Boat Song (Day-O)” during a talent show.

“I should have known better, but I didn’t, and I’m sorry about that,” Trudeau said. “I will ask Canadians to forgive me for what I did. I shouldn’t have done it. I take responsibility for it. It was a stupid thing to do.”

Trudeau said he’s always been very enthusiastic about costumes, “sometimes more than is appropriate.”

“These are situations that I deeply regret,” he added.

The release of the photo could spell more trouble for Trudeau, who polls show faces a serious challenge from Conservative Leader Andrew Scheer.

Trudeau was admired by liberals around the world for his progressive policies during the Trump era, with Canada accepting more refugees than the United States. His Liberal government also strongly advocated free trade.

But the 47-year-old son of the late Prime Minister Pierre Trudeau was already vulnerable after one of the biggest scandals in Canadian political history, which erupted when Trudeau’s former attorney general said that he had unduly pressured her to stop criminal proceedings against a business in Quebec.

Trudeau said he would talk to his children in the morning about taking responsibility.