Prince William liked to shout "the king is in the house" when he DJ'd on holiday before he married Kate, according to her uncle.
Sharing anecdotes about the royal couple's pre-wedding life, Gary Goldsmith revealed that William and Kate spent time at his home in Ibiza when they were dating.
He said: "They've had the full Ibiza experience and they've had a really good time.
"My friend was there who was helping them set up the outdoor DJ and he was teaching William about the beats and how to drop a track. He said the most important thing is to have a shoutout, something to say when you drop a really good track.
"Apparently William's go-to was 'the king's in the house'."
Goldsmith also revealed the very un-royal way he first met the future king, as Prince William was making cups of tea in the Middleton family kitchen. .
Speaking to ITV on The Day Will and Kate Got Married, he said: "The first time I met William was at Carole and Mike's house.
"I walked in to find Catherine cooking, William making cups of tea and Carole, Mike, James and Pippa mooching around the kitchen."
Royal experts have previously said the Middletons gave Prince William the normal family life he did not have, growing up in palaces and surrounded by aides and bodyguards.
While the couple were dating in the early 2000s, Kate's mother warned family members to keep quiet about their relationship amid media speculation.
Before the relationship got out, Goldsmith recalled the warning he got while in a meeting.
He said: "I had a phone call from Carole to mention there was some press was about to land, and just to be aware that Catherine was dating William.
"I was sworn to secrecy but everyone in that boardroom was my friend and the first thing I did was tell them.
"I said 'I think I'm going to be uncle to the future queen of the country'. Everything at that point stopped - and I got totally ridiculed."
That early secret spilling may well be why news of William and Kate's engagement was a surprise to Goldsmith, who said he was "last to know" when William finally popped the question.
William and Kate will mark their 10 year wedding anniversary later this month, on 29 April.
They married at Westminster Abbey in London in 2011, with millions of people around the world tuning in to watch the occasion.
Watch: Kate Middleton Wore a Symbolic Look to Visit Her Wedding Venue With Prince William
Goldsmith, Carole Middleton's brother, told the show: "My mum would have melted on the spot to be there, she would have loved that moment."
"My sister and I come from really humble stock. Mum was a bag of fun, a bag of mischief, bit of a lush, would get somewhere and be the life and soul, and Dad would have to drive us home.
"Dad would work every hour he could to appease Mum. Mum was very driven and motivated."
He said their mother had the nickname "the duchess" adding: "My mum was a proper royalist, we would be at Windsor Castle every chance we got."
John Haley, landlord of the local pub, The Old Boot Inn in Bucklebury said: "Carole and Mike are just a normal family, I seen James, Pippa and Kate growing up through the years
"They used to mix with anybody and everybody."
The Day Will and Kate Got Married is on the ITV hub.
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