Canadian Prime Minister Justin Trudeau apologized Wednesday after a photo emerged of him wearing brownface during a school event in 2001.

"I shouldn't have done it. I should have known better, but I didn't," he told reporters on an airplane. "And I'm really sorry."

It was a photo taken when he was a teacher in 2001, attending an end-of-the-year gala with an "Arabian Nights" theme, he said.

The future prime minister attended the event with friends and colleagues dressed as a character from Aladdin, said Zita Astravas, speaking on behalf of Trudeau's party, the Liberal Party of Canada. He was wearing a turban.

The existence of the photograph was first reported by Time.

Trudeau, 47, was sworn in as prime minister in November 2015. Trudeau, son of Pierre Trudeau, is the first child of a Canadian prime minister to become prime minister himself.