The photo was taken when the Canadian prime minister was attending an “Arabian Nights”-themed gala while working as a teacher in Vancouver.  Justin Trudeau, wore brownface makeup to the party.  TIME has obtained a photograph of the incident.

Daily Beast says Canadian Prime Minister Justin Trudeau admitted he “made a mistake” late Wednesday after a photo surfaced of him wearing brownface makeup to an “Arabian Nights”-themed gala at the Vancouver private school where he taught in 2001.

Photo / The Time

The picture, found in West Point Grey Academy’s yearbook and published by TIME, shows Trudeau with his face, neck and hands darkened—along with him wearing a turban and robes.  While he was not the only one pictured in costume at the gala, he appeared to be the only one pictured in brownface.

“Obviously I regret that I did it, I'm really sorry I did it,” Trudeau told reporters Wednesday evening.  “I take responsibility for my decision to do that.  I should have known better...  I didn't know it was racist at the time.”

The photograph appears in the 2000-2001 yearbook of West Point Grey Academy, a private day school where Trudeau was a teacher.  The photograph has not been previously reported.

Earlier this month, TIME obtained a copy of the yearbook, The View, with the photograph of Trudeau in brownface from Vancouver businessman Michael Adamson, who was part of the West Point Grey Academy community. Adamson was not at the party, which was attended by school faculty, administrators and parents of students. He said that he first saw the photograph in July and felt it should be made public.

TIME says this is a critical moment for Trudeau, who began his re-election campaign on Sept. 11 under the cloud of a scandal over whether he pressured his then-attorney general to drop corruption charges against a large Canadian engineering firm.