King Charles III was given a heartfelt standing ovation in Canada's parliament in Ottawa after a historic speech in support of the country staying "strong and free".

Outside the Senate building later, another voice from the crowd shouted: "Thanks for coming King Charles" in a voice full of emotion - as the King himself had sounded at the end of his speech.

But what was never mentioned was what the speech was really about: US President Donald Trump.

There was a promise to "protect Canadians and their sovereign rights", but with diplomatic discretion, there was no mention of who might be threatening the country's independence.

Claims by Trump that Canada would be the 51st US state hung over this speech, but his name was never uttered.

Not when the speech talked of the virtues of "open trade" (ie, not tariffs) or when it talked of a "critical moment" in which "democracy, pluralism, the rule of law, self-determination and freedom" must be protected.

And there was no one named as making it necessary to guard the country's "fundamental rights and freedoms".

There might even have been an olive branch, with a promise by the Canadian government to do more to stop fentanyl crossing the border, a drug that was the subject of accusations by the US administration. But there was no mention of Trump by name.

The opening of parliament followed a general election in which Mark Carney had been brought to power on a wave of anti-Trump sentiment.

The speech was written on the advice of the Canadian government, but there was a great deal of symbolism in the King reading it out. The King of Canada was in town.

Inviting King Charles seemed to have paid off for Carney, who afterwards said how well the speech had been delivered. "Our sovereignty is strong," said Carney.

From the parliamentarians inside the packed chamber to the crowds pressed up against the railings outside, the King's visit was seen as sticking up for Canada when it was under pressure from its bigger neighbour.

Compared with openings of Parliament in Westminster, this was a more dressed-down affair. No crowns or robes, with the King looking businesslike in a suit.

Showing this really is a relaxed country, the former PM, Justin Trudeau, was wearing a pair of green trainers.

A theme of this brief royal visit has been paying respects to the First Nations people and the King noted that parliament was meeting on the territory of the Algonquin people.

Among the parliamentarians were many representatives of First Nations communities, dressed in traditional outfits and spectacular headdresses. The speech, delivered in French and English, made a virtue of the country's diverse roots.

Before the King's arrival, there was an unmistakable sense of anticipation with the sober lawmakers taking a few quick selfies before the big royal moment. There was that nervous buzz ahead of something important.

There would be a long list of government plans and policies, but there was a bigger historic feel to events, with a huge media encampment outside and crowds lining the streets.

The opening of parliament took place in Canada's Senate, which is currently using temporary accommodation while its own building is renovated.

The building being used by the Senate used to be Ottawa's main railway station. You could still see how the floor of the chamber had once been the station concourse.

A different type of king, Elvis Presley, had come through here on a train journey in 1957. If there were suspicious minds here about whether King Charles would stand up for Canada, he was able to put that to rest.

In the warm Ottawa sunshine, there were crowds sending their own message by turning out to see the King. Even a fleeting visit here soon shows how deeply people have been upset by their near neighbours and allies in the US.

There seemed to be a genuine sense of relief that the King was there and showing support. The King also looked pleased, standing outside the Senate, holding a quick walkabout while a motorcade of oversized black cars was waiting to drive him away. He later spoke of the "warmest of welcomes".

He waved before he left, having a last look around, towards the crowds and towards the cameras. Was there someone south of the border watching?

The US state department spokeswoman Tammy Bruce responded to the speech: "I'm a fan of King Charles. And of Prince William and Princess Kate. I think they're a great family."