Prime Minister Justin Trudeau had a private audience with the Queen Wednesday morning. But this isn't the first time a prime minister with the last name Trudeau met Her Majesty. Nearly 40 years ago, his father caused a stir when he famously pirouetted behind the monarch's back.

Retired Canadian Press photographer Doug Ball took the iconic photo of then-prime minister Pierre Trudeau during a photo session of several leaders at Buckingham Palace on May 7, 1977. Ball had been assigned to cover the G7 Summit in London, which Trudeau and other leaders were attending.

The photo, which shows the prime minister spinning with his arm extended up in the air while the Queen walks away, caused an international sensation once it was printed.

However, Ball said it was by chance that he got the famous shot.

"There was one photographer per country allowed," he told CTV's Canada AM. "We were given a little pass to go into the palace, and we were all lined up along the wall…I slid along one side because Trudeau was on the left, and I wanted to get him bigger in the photo. I didn't care about the others."

Ball said as the other leaders began departing for dinner, he noticed Trudeau looking at his feet. The then-prime minister then looked up, executed a spin, then shrugged his shoulders and walked off to join the others for dinner.

"I just fired… because I thought it was over," Ball said of the moment he took the photo, noting that his camera wasn't even focused at the time.

Ball later gave the film to a runner, who had it developed at a nearby photo lab. He said he only realized what kind of photo he had taken after it was published by The Associated Press, who erroneously captioned it as "Prime Minister Trudeau arrives late for dinner."

Two years later, during an election campaign stop in Winnipeg, Ball said he seized the chance to ask Trudeau about the pirouette seen-round-the-world. He asked the then-Liberal leader if he had been drunk during the meeting with the Queen.

"(Trudeau) said, 'No, no… I had a couple of drinks in there, but I wasn't drunk,'" Ball said, with a laugh.

Wednesday’s audience with the Queen isn’t the first time the younger Trudeau met the monarch. Earlier in the day, he described what it was like to meet her when he was young boy in the late 1970s, when his father was in office.

"She was always lovely and gracious. She was very tall which points out how little I was at the time. They were nice moments because I knew how much my dad liked her," he said in notes released from the Prime Minister's Office. "You could tell my father was really proud to be introducing his son to the Queen."