Last year on their first wedding anniversary, Mark took to social media to pay tribute to his wife.
"12 months ago I married this amazing woman. It’s been tough at times due to work commitments but an amazing journey she is truly one in a million," he wrote.
"I married the girl of my dreams we made our vows and created a new life together. No one said it will be easy, but true love always prevails."
While Mark doesn't often discuss his marriage in the press, the 56-year-old regularly posts sweet photos and videos of the pair to his 343,000 Instagram followers.
The pair often film their gruelling workouts together, where Mark puts Julie through her paces using his years of military training.
Julie is the founder of eco-conscious footwear label Deux Mains, which she described as a "brand that fights poverty through the sustainable productions of high fashion footwear, handbags and accessories".
On In International Women's Day this year, Mark praised Julie for her company's work with helping people in Haiti.
"My beautiful wife empowering women and men @deuxmainsdesigns with employment in ethical fashion," he said.
Due to Julie residing in Florida and Mark constantly travelling for the UK version of the show SAS Who Dares Wins, the pair often spend long stretches of time apart.
"Almost time to be reunited," Mark captioned a recent photo of them, adding that "time spent together is never wasted".
In April 2019, Julie took to Instagram to gush over her husband ahead of the fifth season of SAS Who Dares Wins airing in the UK.
"I am so proud of him and one of the many reasons I love @billingham22b so much is because he has ALWAYS used his experience and knowledge to help others," she penned.
While the loved-up couple don't have any children together, they often share adorable snaps of their British Bulldog Alfie.
In April last year and after a month of separation due to the pandemic, Julie was granted permission to fly to the UK from the US to be with Mark.
"Now we sit in quarantine and get to celebrate together all the moments we missed being apart last month... mainly our 1 year wedding anniversary," she wrote.
"We feel so grateful and are enjoying every moment together."
Before settling down into married life, Mark worked as a bodyguard for some of the world's biggest A-listers – including Tom Cruise and Kate Moss – and eventually becoming a permanent fixture with Brad Pitt, Angelina Jolie and their six children.
"Angie and Brad are very worried about who goes near the children," he told Woman's Day last November.
"Working with such high-profile celebrities was great. I learned a lot of lessons from them, they learned a lot from me and the beauty of working together was the mutual respect.
"They respected what I had to do and I respected what they had to do, and it worked fine and created a very professional understanding."
Following his 27-year career with the elite British Special Forces, Mark was awarded an Order of the British Empire from the Queen.
"It was more a proud moment for my mum and dad who had no idea why I was receiving the award until the citation was being read out as I marched towards Her Majesty," he reminisced.
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