
Just because Prince William has grown up as a member of the Royal Family doesn't mean he hasn't made a royal faux pas on occasion and he's spoken publicly about one of these "awkward" mistakes before. It happened during his first time attending one of the annual Diplomatic Corps receptions and the late Queen Elizabeth's reaction was rather surprising.
These events bring together ambassadors, diplomats and high commissioners from all over the world. The prospect of meeting so many important people all at once would be daunting for anyone, so it's understandable that Prince William finds them a "diplomatic minefield".
"You have to be careful what you say and who you say it to," he said on the Our Queen at Ninety documentary in 2016. "My first diplomatic reception was a little bit awkward. I may have mentioned to two particular countries who don't get along, I got the wrong one…muddled up."

Admitting that the mistake was "quite embarrassing", the future King went on to share that his grandmother was "very cool about it". He added, "She laughed about it and thought it was quite funny. Luckily, there wasn't any [fallout] but it was ok."
Had there been fallout from the mix-up perhaps Queen Elizabeth might have felt differently, though learning the ropes of royal life takes some time and she would no doubt have been the first one to smooth things over if needed. This was a valuable diplomatic lesson for Prince William to learn and elsewhere in the documentary he said his granny was "always on hand for advice and support".
Although actual mistakes like his aren't ideal, in general he added that "it's as much about doing it [royal duties] our own way as it is about getting it right".

Her "cool" reaction at the Diplomatic Corps reception likely calmed her grandson and Queen Elizabeth is famous for using her dry sense of humour to make light of faux pas.
In May 2007 she was welcomed to the White House by then-President George W Bush and his speech significantly added to her age. The President accidentally remarked upon how she was there to celebrate the US bicentennial in 1776 rather than 1976.
A few days later at a dinner held at the British Ambassador's residence, the Queen gently teased him by saying, "I wondered whether I should start this toast by saying, 'When I was here in 1776...'" which sparked plenty of laughter. In his own speech, the President confessed, "Your Majesty, I can't top that one."

Another hilarious moment she reacted to with grace and humour came when she visited the US in 1991 and addressed a crowd with pretty much only her hat visible over the top of the podium. Queen Elizabeth was around 5ft3 and the podium clearly wasn't suited to this, but she carried on regardless and quipped about this the next day.
Whilst talking at the House of Congress, she began her speech by saying, "I do hope you can see me today from where you are…" which prompted roars of laughter and standing applause. If anyone knew a good one-liner it was Queen Elizabeth and mistakes are all part of royal life.