Former Royal butler Paul Burrell says there is one thing that staff were told not to do when working with Queen Elizabeth II. Burrell, 67, began working as a footman at Buckingham Palace when he was just 18 years old.
A year later he started working as one of the personal footmen - who do tasks such as waiting tables or attending coaches - for the Queen. He later went to work with the-then Prince Charles and Princess Diana at Highgrove House in Gloucestershire.
He remained working as a butler for the princess until she died in 1997. He once claimed she described him as the "only man she ever trusted".
Now Paul, who spent a decade with the Queen, says there was one thing he was told "never" to do while serving her. He made the revelation in his new book, The Royal Insider: My Life with the Queen, the King and Princess Diana.
Paul wrote: "I had progressed beyond empty cups to potatoes and gravy. We were always told never to look at the Queen or to stare at her: never look her in the eye, always look down."
While Paul managed to climb through the ranks working for the Queen, he admits he was "nervous" when he first met her. The first moment he laid eyes on her, he recalls he was carrying a silver tray with 20 Royal Worcester coffee cups, saucers, and gilt spoons.
He says he walked into the dining room and spotted the Queen chatting to the Queen Mother, and Charles. Around 30 members of the Royal Family were at the event.
Paul recalls starting to feel nervous as he entered the room. He continues: "Then my nerves got the better of me and the cups and saucers all started to rattle.
"I will never forget the noise. All I had to do was stand behind the Queen and the pages would come to me and collect the cups."
Paul explains the rattling was "so loud" that the Queen turned around to "look at what the commotion was". The Queen simply smiled back, marking Paul's introduction to the monarch.
And while their first meeting might not have gone how the former butler planned, Paul believes the Queen "got to know his face" along with the other footmen who waited on her at "meet the people" lunches in the 1844 room.
After Diana's death in 1997, Paul's career has pivoted towards writing. He has now released a number of books looking at his time in Buckingham Palace, Highgrove House, and latterly Kensington Palace.
His 2003 memoir, A Royal Duty, led to a fallout with Prince William and Prince Harry. They reportedly called the book a "cold and overt betrayal" to their mother.
His latest book, The Royal Insider: My Life with the Queen, the King and Princess Diana, was released last week.