Former U.K. prime minister Boris Johnson says Canada's exclusion from AUKUS — the trilateral security pact between Australia, the United Kingdom and the United States — was not intended to send any particular message.

In a wide-ranging exclusive interview on CTV's Question Period, airing Sunday, Johnson told host Vassy Kapelos he now thinks it could be a "good thing" if Canada joined the group as it evolves, but that it was originally started specifically to address the complexities of a submarine purchase deal.

"It arose in a very unique way," he said. "There was no intention to exclude anybody."

AUKUS was first announced in September 2021 and was created to help Australia develop nuclear-propelled submarines, as Indo-Pacific countries worked on plans to deal with an increasingly adversarial China.

Johnson was serving as the prime minister of the U.K. at the time.

When asked by Kapelos whether Canada's exclusion was "a slight in any way," Johnson said "no."

"It wasn't Canada that was cheesed off," he said. "Canada was fine."

"It was the plaster came off the ceiling in Élysée Palace," he added, explaining that Australia originally intended to purchase submarines from France, but that they were the "wrong type" and "too noisy," so the Australians approached the U.K.

The U.K. then had to involve the U.S. because of nuclear agreements between the two, Johnson said.

"When it comes to AUKUS, this was a deal that was done, basically, because of the Australian need for a different type of submarine," Johnson said. "That was the history of it."

Last June, U.S. National Security Council spokesperson John Kirby also told Kapelos in a CTV's Question Period interview there were to include Canada.

Meanwhile, The Canadian Press had reported at the time that the Canadian military and other defence experts raised concerns about Canada being shut out of the group.

On Monday, following the release of a new defence policy document, Canadian Prime Minister Justin Trudeau said at a press conference that Canada has had "excellent conversations" with all three current AUKUS members around joining the security pact for its "phase two."

In his interview, Johnson also discussed the U.S. presidential election, saying there are "reasons for optimism" with a potential second Donald Trump presidency, despite concerns his return to the White House could threaten U.S. aid for Ukraine.

He also discussed climate change and the U.K.'s pledge under his leadership to achieve net zero by 2050, saying politicians should not toss aside their climate commitments in order to address the cost of living crisis.

You can watch Johnson's full exclusive interview in the video player at the top of this article.

With files from CTV's Question Period Senior Producer Stephanie Ha and CTVNews.ca's Senior Digital Parliamentary Reporter Rachel Aiello