(CNN) President Donald Trump started handing out his personal cell phone number to world leaders shortly after he took office last year, leading to one-on-one calls that even top White House aides did not know about, according to a report in The Washington Post.

White House aides learned of an April 2017 call between Canadian Prime Minister Justin Trudeau and Trump only after a standard summary was issued by officials in Canada , according to the Post, which said its report was based in interviews with US and European officials who spoke on condition of anonymity.

Conversations with world leaders are required by federal records law to be routed through the Situation Room, the Post reports. Such calls are typically heavily prepared for and monitored by the White House; the national security adviser briefs the president, and regional experts provide prepared talking points. The national security adviser then remains by the president's side throughout the call, and a transcript of the call is distributed to key White House aides, who issue a public readout.

When it came to the call with Trudeau, US officials had to rely on Trump's recollection. The short official statement released simply said it was "a very amicable call."

The White House did not immediately respond to CNN's request for comment.

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