When it comes to families, we all have our own dynamics and one trait that most can relate to is some good natured teasing. The Royal Family may be, well, royalty, but that doesn't mean they aren't a normal family in many ways, too. And, it turns out, there is one thing in particular that Prince William makes fun of his dad for - even if he is now The King.

According to the royals' former butler Grant Harrold, there was a 'random thing' in particular that The Prince of Wales used to make jokes about. The King famously owns a prized Ast0n Martin which he received as a 21st birthday present from his parents. As we know, cars can be extremely damaging to the environment due to the fumes they emit but The King, being a life-long eco-advocate, came up with an ingenious (if bizarre) solution.

barry, wales february 21: prince charles, prince of wales is seen next to his aston martin db6, during his visit to the new aston martin lagonda factory on february 21, 2020 in barry, wales. (photo by rebecca naden wpa pool/getty images)
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King Charles and his Aston Martin.
criencester, united kingdom june 17: (embargoed for publication in uk newspapers until 24 hours after create date and time) prince charles, prince of wales accompanied by camilla, duchess of cornwall arrives, driving his 1969 aston martin db6 volante, to play in the burberry cup polo match at cirencester park polo club on june 17, 2005 in cirencester, england. (photo by max mumby/indigo/getty images)
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'The interesting thing about [the car] is that he had it modified in 2008 so it runs on wine and cheese,' explains Grant, who worked for the Royal Family between 2007 and 2011. 'He’s so conscious of the environment, and was long before it became mainstream. He was always looking for ways he could to protect the environment, it’s something he’s so passionate about.'

According to Grant, the unusual modification became the ammunition for some good-natured teasing; 'Prince William used to mock his dad for it a lot, in a loving way of course, but it’s just such a random thing to do.'

ayrshire, united kingdom march 05: prince charles, prince of wales, known as the duke of rothesay, catherine, duchess of cambridge, known as the countess of strathearn, and prince william, duke of cambridge, known as the earl of strathearn, when in scotland during a visit to dumfries house on march 05, 2013 in ayrshire, scotland. the duke and duchess of cambridge braved the bitter cold to attend the opening of an outdoor centre in scotland today. the couple joined the prince of wales at dumfries house in ayrshire where charles has led a regeneration project since 2007. hundreds of locals and 600 members of youth groups including the girl guides and scouts turned out for the official opening of the tamar manoukin outdoor centre. (photo by danny lawson wpa pool/getty images)
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Grant, speaking via Select Car Leasing, admitted that the staff also saw the funny side of the environmental amend saying, 'We couldn’t believe it when we found out, we used to joke about it a lot in the staff room.'

While Prince William might poke fun at his dad about his Aston Martin, it doesn't mean he doesn't admire it. However, The King is 'very, very protective of that car,' says Grant. 'He never let anyone else drive it. It was a big issue as I remember both William and Harry wanting to drive it, but he wouldn’t let them.'

london, england april 29: prince william, duke of cambridge and catherine, duchess of cambridge drive from buckingham palace in a decorated sports car on april 29, 2011 in london, england. the marriage of the second in line to the british throne was led by the archbishop of canterbury and was attended by 1900 guests, including foreign royal family members and heads of state. thousands of well wishers from around the world have also flocked to london to witness the spectacle and pageantry of the royal wedding. (photo by julian finney/getty images)
Julian Finney
london, england april 29: prince william, duke of cambridge and catherine, duchess of cambridge drive from buckingham palace to clarence house in a decorated vintage aston martin sports car on april 29, 2011 in london, england. the marriage of the second in line to the british throne was led by the archbishop of canterbury and was attended by 1900 guests, including foreign royal family members and heads of state. thousands of well wishers from around the world have also flocked to london to witness the spectacle and pageantry of the royal wedding (photo by jeff j mitchell/getty images)
JEFF J MITCHELL

However, there was one very special occasion when King Charles relented and made an exception for his son. 'He let William and Kate borrow it on their wedding day, and that was a big deal.'