Queen Elizabeth isn't allowed to dance in the Royal Box at the Royal Albert Hall.
The 95-year-old monarch has appeared in the box at the historic London venue countless times over the years, but a 150-year-old document means she can't get up and boogie likes other punters.
As quoted by the Daily Mirror newspaper's Diary column, the venue's CEO Craig Hassall said: "It's in the constitution, you're not allowed."
There was one moment the rule was nearly broken when Nelson Mandela was the guest of honour at the 'Two Nations Celebrate' concert in 1996.
He arrived in the UK for a four-day state visit, with Phil Collins, Tony Bennett and Quincy Jones performing at the special show, which was raising money for the Prince's Trust.
The Queen, Prince Charles and Mandela's daughter Zenani Mandela-Diamini all in attendance, but the policy means people in the box aren't allowed to dance.
However, artistic director Lucy Noble told the RocknRoll Business podcast: "The entire Royal Family were here in the Queen's box with Nelson Mandela.
"It was a complete party atmosphere - the whole Royal Albert Hall was up dancing. But there is this policy in the Queen's box that you can't dance.
"They were all sat there. But Nelson Mandela gets up and does this really cool dancing. Then the Queen stood up and held her handbag and just stood there. It was hilarious, that moment."
Meanwhile, Buckingham Palace recently announced a pudding competition to honour the Queen as part of her Platinum Jubilee celebrations, which mark the monarch's 70 years on the throne.
Brits over the age of eight have been invited to "create the prefect pudding recipe" for the contest, in association with upmarket London department store Fortnum & Mason.
Five shortlisted finalists will then have their hard work judged by a panel comprised of Dame Mary Berry, Monica Galetti and Mark Flanagan, the Head Chef at Buckingham Palace, for the grand prize of their offering being sold to the public and featuring at meals during the Jubilee weekend.