When meeting members of the Royal Family, there is often a protocol people are invited to follow – but that occasionally goes out the window.
Some celebrities have been left red-faced during their encounters but have eventually gone on to laugh the awkward moments off.
Nowadays, the likes of the Prince and Princess of Wales have been more than happy to pose for selfies and be less formal with the public, but that's never stopped some people.
Meanwhile, it was thought of as more polite to follow protocol when stars met the likes of the late Queen Elizabeth and the now King Charles and Queen Camilla.
Days before the Coronation of King Charles and Queen Camilla, we take a look at some of the most awkward encounters celebs have had with members of The Firm.
Lionel Richie
Having been announced as a performer at this weekend's Coronation Concert at Windsor Palace, Lionel Richie is no stranger to royalty.
Ahead of the grand event, the singer attended a garden party at Buckingham Palace held by Their Majesties and was attended by the Duke and Duchess of Edinburgh, as well as the Duke of Kent and Duke and Duchess of Gloucester.
But Lionel appeared to be more than relaxed in front of Queen Camilla which left some royal watchers bewildered.
As the Queen greeted him, the All Night Long singer extended his arm to shake the Queen's hand before gently patting her on her arm on several occasions.
Royal etiquette states that you are to wait for a member of the Royal Family to extend their own hand before shaking.
Spice Girls
The Spice Girls were known for tearing up the rulebook after finding fame and royal protocol certainly didn't bother them.
Sporty, Scary, Posh, Ginger and Baby rubbed shoulders with royalty on multiple occasions and Prince William appeared to be a fan of theirs.
But the girls tested the boundaries during a meeting with the then Prince Charles at the premiere of their movie Spice World in 1997.
Following their encounter, it was claimed that Geri Horner had pinched Charles on the bum but in 2016, she set the record straight.
Speaking to The Times, Horner said: "Patting him on the bottom was against royal protocol but we're all human.
"There was a lot of nervous energy...young women, happy antics."
Tom Hiddleston
During a meeting with the then Camilla, Duchess of Cornwall in 2016, Tom appeared to show his affection for the now Queen.
The Marvel actor wrapped his arm around Camilla and appeared to hug her during an appearance at an event as he posed with Camilla and Chris Evans.
But it appears that the Queen took it in her stride as they posed together at Radio 2's headquarters as she joined the judging panel for the 500 Words children's competition.
While this is often frowned upon, a spokesperson for Clarence House said at the time: "I think she quite enjoyed it," adding that it was a "warm moment" and she and Tom "got on very well and had a very nice chat together."
Michelle Obama
Being a mum to two young girls, former First Lady Michelle Obama was no stranger to being hands-on.
And during a meeting with the late Queen Elizabeth in 2009, this was no different as she placed her hand on the late monarch's shoulder.
Writing in her memoir, Becoming, Michelle explained that Her Majesty didn't seem too bothered by the breach and instead, warmed to the idea.
"Forget that she sometimes wore a diamond crown and that I'd flown to London on a presidential jet; we were two tired ladies oppressed by our shoes," she said, before adding: "I then did what's instinctive to me anytime I feel connected to a new person, which is to express my feelings outwardly. I laid a hand affectionately across her shoulder.
"I daresay the Queen was okay with it, too, because when I touched her, she only pulled closer, resting a gloved hand lightly on the small of my back."
Margot Robbie
As Hollywood royalty, it's no surprise that Australian-born Margot has royal connections.
Apart from being born in a Commonwealth country, it appears Robbie has friends in high places – well, friends who are a member of the Royal Family.
While filming Suicide Squad, she was dared to prank call Prince Harry by her co-star, Cara Delevingne.
"I said, 'We can't prank-call royalty'," she told The Sun, before going on to say: "Anyway, we did, and he was so cool with it."
Lewis Hamilton
Formula One champion Lewis met the late Queen on several occasions, including during a private lunch at Buckingham Palace.
But things turned sour when Lewis didn't follow the royal protocol when talking around the table and the Queen later corrected him on the proper etiquette at a dinner table.
During an appearance on The Graham Norton Show, he said: "I was excited and started to talk to her, but she said, pointing to my left, 'No you speak that way first, and I'll speak this way and then I'll come back to you.."
However, he later said the Queen was a "sweet woman" and explained they "talked about how she spends her weekends, houses and music".
