But fewer people know about the youngest Middleton: 29-year-old James, who's making his way in the business world as the head of a 100% serious, personalised marshmallow company called Boomf.
Here's a look at James's life both before and after his family became quasi-royalty.
James, 29, is the youngest Middleton sibling. He grew up with Kate and Pippa in Bucklebury, Berkshire and attended the boarding school Marlborough College.
The official Royal Wedding group photograph in the throne room at Buckingham Palace with the Duke and Duchess of Cambridge. Front row (L-R): Grace van Cutsem, Eliza Lopes, Prince Philip Duke of Edinburgh, Queen Elizabeth II, Margarita Armstrong-Jones, Louise Windsor, William Lowther-Pinkerton. Back Row (L-R): Tom Pettifer, Camilla Duchess of Cornwall, Prince Charles, Prince Harry, Michael Middleton, Carole Middleton, James Middleton and Philippa Middleton (Getty Images)
It was around this that time news outlets were first reporting Kate and Prince William's budding romance — and James took extreme measures to minimize rumors and chatter.
"I used to be first up in the morning to make sure I could get to the papers and rip out any stories about my sister, so nobody would see them and there would be no conversations about them," he recently told the Daily Mail.
Pippa Middleton arrives at church to marry James Matthews
But school was never James's strong suit. He's dyslexic, and knew that university wasn't for him. So he dropped out of Edinburgh University after one year.
"I knew that that mouthful of academic prescription was not going to do it for me," he told GQ. "My dream, which came to me when I was flying back up to Edinburgh after a weekend home, was to build a cake empire."
In 2007, he launched the Cake Kit Company, which provided customers with DIY kits for festive party cakes.
(thecakekitcompan.com)
Sadly, James's "cake empire" wasn't to be: The company would eventually dissolve in May 2015.
In the meantime, his older sister Kate got married to Prince William in a ceremony watched by an estimated two billion people worldwide.
James was just 23 years old on the day of the wedding.
(AP/Joel Ryan, Pool)
Suddenly, he and sister Pippa were getting lots more attention from the media — and not all of it was good.
After the wedding, a number of compromising photos of James were leaked online. Outlets that published the photos got threatening legal emails demanding the photos be taken down — but it turned that the "lawyer" who sent those emails was just James himself.
The photo scandal didn't look good — especially since it wasn't James's first embarrassing brush with the media. GQ reported that he was photographed drunkenly stumbling out of a club on his 21st birthday a few years earlier.
But James continued working and making public appearances.
He and Pippa frequently stepped out as a pair, since they shared an apartment together. Here they are at Wimbledon in 2013.
In 2013, James was first photographed with British media personality Donna Air.
(Joel Ryan/Invision/AP)
Air was married once before and has a 13-year-old daughter, Freya. "I love Donna very much and Freya is very much part of Donna," James told the Daily Mail. "I love them both equally."
2014 brought about a major style evolution for James: He grew a beard.
"My mother looks at it and says, 'When are you going to get rid of it?'" he told the Daily Mail. "But then that's because she wants me to be her little boy."
More importantly, he'd finally rebounded after the shutdown of his cake business. In 2014, he appeared on "Good Morning America" to promote his new venture, Boomf.
RW/MediaPunch/IPX (RW/MediaPunch/IPX)
It's a service that allows you to print graphics and personal photos on marshmallows. He's raised "£1.5 million ($1.9 million) of recent investment".
"When you see yourself on a marshmallow, or your loved one or your pet, you have a little moment with that little marshmallow. There aren't many products in the world like that," he told the Cut. "I'm very much surrounded by [marshmallows], but I still love them [...] Marshmallows are sort of like an essential candy. They're pillows of sweetness."
James has told reporters that Boomf is doing well financially. He's also described himself as a "new age Willy Wonka."
When he's not working, he pursues an interesting set of hobbies: He keeps bees, restores old tractors and Land Rovers, and breeds dogs.
Reuters/Andrew Matthews, Pool (Reuters/Andrew Matthews, Pool)
He has even said that "vintage tractor magazines" are his guilty pleasure.
He also spends time with his nephew and niece, Prince George and Princess Charlotte.
"I just want to be the best uncle possible," he once told "Good Morning America." "Like any uncle wants to be, I want to be the cool uncle. The fun uncle. That's what sort of I'll always try and be."
(Facebook/The Royal Family)
And his relationship with Air appears to be going strong. They were most recently photographed together in November 2016.
Mostly it seems like James Middleton wants to forge an identity separate from his famous sisters.
"I work incredibly hard — just like every other person in business," he told digital magazine TYD in 2015. "Aside from the fact that yes, I am the brother of someone very important, I am, at the end of the day, just James."
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