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The Liberal Party leader's campaign has been upended since Time magazine on Wednesday published an image of him with his face blackened at a 2001 "Arabian Nights" party when he was a 29-year-old teacher at a private school in Vancouver.
Other images have since emerged and Trudeau said he was "wary" of ruling out the existence of even more because he could not remember those that already come to light.
Answering questions from Winnipeg, Manitoba, Trudeau said that his privilege as the white son of former Prime Minister Pierre Trudeau had come with a "blindspot."
"I come from a place of privilege and I have endeavoured in my life to put the advantages and opportunities I've been given to serve this country, to fight for people's rights," he said.
"I have to recognise that I've let a lot of people down with that choice (to wear blackface) and I stand there today to reflect on that and to ask forgiveness."
During his apology, he also admitted to performing Day O, a traditional Jamaican song made famous by Harry Belafonte, in brownface during a high school talent show years earlier.
The Canadian Broadcasting Corp. then published a picture from that performance that was confirmed as authentic by a spokeswoman.
Also, Global News put out a video showing Trudeau again in dark make-up making faces and sticking his tongue out. It was not immediately clear when that video was from.
"We can confirm that it is him and it's from the early 1990s," a Liberal official said of the video without clarifying exactly when the video was shot.
Earlier, Trudeau held a conference call for all his 338 candidates at the election.
"The Prime Minister expressed his apology and regret and said this happened 20 years ago," one Liberal on the call said. "He said this is the moment for us to continue to work together to understand the pain of people who are on the receiving end of racism and stereotypes."
Even before the scandal, the race going into the October 21 vote was tight. But the release of the bombshell images could be a turning point, in part because Liberals have traditionally attracted support from immigrant communities.
Trudeau has championed racial equality and diversity as Prime Minister, and has three prominent ministers of Indian descent in his Cabinet.
"I'm not that person anymore," he said. "I'm someone who understands the deep hurt cause by actions like that to people who live with discrimination every single day."
Greg Fergus, a black Liberal legislator from Quebec, said Trudeau had called him before the story broke on Wednesday to apologise.
"I don't believe that anybody has ever lived their lives without making errors," Fergus told reporters in Ottawa, saying Canadians should focus on "all the amazing things we have done for diversity."
Conservative Party leader Andrew Scheer, Trudeau's main rival, said the video was proof that the Prime Minister had lied during his apology on Wednesday because he only mentioned having appeared in blackface twice.
"He did something that was racist and he lied about the extent of such activities," Scheer told reporters in Saint-Hyacinthe, Quebec.
But Scheer also acknowledged that the Conservatives had leaked the video to Global News.
Trudeau has seen his once sky-high popularity hurt by a series of missteps, including a ruling last month by a top watchdog that he had breached ethics rules by pressuring the former justice minister to ensure a major construction firm avoid a corruption trial.