Justin Trudeau's first audience with the Queen: what happens, and why

It's a rite of passage for any new Canadian prime minister: the trek to Buckingham Palace for a formal tête-à-tête with the Queen.

And as he embarks on his second world tour in just two weeks, Prime Minister Justin Trudeau was received by Her Majesty today at the royal residence in the heart of central London. She granted him — in the parlance of the monarchy — an "audience."

The two had a private conversation, free from the menagerie of political advisers and palace staff that usually accompany the two leaders. And because such proceedings are strictly confidential, it is difficult to know what happened beyond the gilded doors of the royal reception room.

What we do know is that the Queen does not offer political commentary — her position demands nonpartisanship. Rather, she serves as a sort of sounding-board for prime ministers as they grapple with the challenges of governing.

Vernon Bogdanor, a professor of government at King's College, London, and an adviser on the Broadway play The Audience, a fictional depiction of such meetings, says the Queen will likely draw on her historical knowledge to advise the 42-year-old fledgling leader.

"The Queen might well say to the prime minister: 'A measure similar to the one you are suggesting was proposed around 25 years ago when you were still at university. You probably do not remember, but it did have some bad results. Perhaps you might have a look at what happened and discuss it with your colleagues," Bogdanor says.

Trudeau would not be obliged to accept her advice, but he could file it away for consideration when drafting legislation.

One British prime minister, James Callaghan, characterized an audience with the Queen as something akin to visiting a psychiatrist.

The Queen's longest-serving British prime minister, Margaret Thatcher, wrote in her memoirs that the visits are much more than a chance to share a pot of tea.

"Anyone who imagines that they [the audiences] are a mere formality or confined to social niceties is quite wrong; they are quietly businesslike and Her Majesty brings to bear a formidable grasp of current issues and breadth of experience," Thatcher wrote.

Justin Trudeau, no stranger to royal family

It's a daunting task for any new prime minister: impress a monarch who has quite literally met hundreds of heads of state. After all, Trudeau is the twelfth Canadian prime minister to serve under the Queen since she ascended to the throne in 1953.

"If anybody is going to be on their toes, it's going to be the prime minister," said Robert Finch, the dominion chairman of the Monarchist League of Canada. "She will have done all her homework. Canadian prime ministers have always commented on just how well-informed and knowledgeable the Queen is about Canadian affairs."

The monarch is well briefed by her Canadian secretary, Kevin S. MacLeod, on such matters. And she is also known to pore over cabinet documents, parliamentary papers and reports from ambassadors.

But there was a natural icebreaker for Trudeau: He's already met her, a perk that comes with being the son of a man who was one of the country's longest-serving prime ministers.

"There were lunch hours where I wouldn't eat at school because we had to rush home to have lunch with the Queen," Trudeau recounted in an 2013 interview. "At the same time, it was instilled upon us that this was a privilege and a responsibility, and nothing made us better than anyone else — maybe randomly luckier."

Pierre Trudeau, the unlikely monarchist

The Queen and Pierre Elliott Trudeau had a relationship complicated by his republican leanings.

As a student, he penned an essay criticizing Canada's relationship with the British Empire as a relic of our colonial past. Later, as prime minister, he was famously caught on camera doing a pirouette behind the Queen as they took part in a G7 summit in London.

But his attitudes softened with time as John English, one of Trudeau's biographers, recounts in his book Just Watch Me. When faced with the realities of governing in an era polarized by two superpowers, Trudeau learned to appreciate the Commonwealth of Nations as a multilateral force for good.

But more than that, his relationship with the Queen warmed considerably, going so far as to say she did "a first rate job" as head of state, and that he was impressed by her attention to events in Canada.

The Queen was equally smitten, inducting the one-time republican rebel into the Order of the Companions of Honour, a prestigious club that never has more than 65 members at one time and who are chosen for their exceptional service to the Commonwealth.

The younger Trudeau, for his part, has said that the role of the Queen in Canada will see little change under his leadership.

In announcing the meeting, Trudeau promised that "Her Majesty will remain an integral part of our country's progress and future."

And the timing of the meeting may signify that Trudeau has taken that pledge seriously. Whereas it took Stephen Harper more than half a year after his election to meet the Queen, Trudeau is making the visit after only a month on the job.

"He's made a point to meet the Queen very early in his mandate, it's certainly a good signal," Finch says. "And it's hopefully the first [meeting] of what will be many more to come."