The Duke of Sussex has since made light of his mother's twee habit. Speaking in the documentary, Diana, Our Mother: Her Life and Legacy, the father-of-two said: "I genuinely think she got satisfaction out of dressing myself and William up in the most bizarre outfits – normally matching.
"It was weird shorts and little shiny shoes with the old clip-on. Looking back at the photos it just makes me laugh and I think, 'How could you do that to us?'"
Keep scrolling to discover their sweetest twinning moments…
1/5
Dungarees for days
Princess Anne and her family are regulars at the Royal Windsor Horse Show.
Back in 1983, sibling duo Zara and Peter melted hearts as they attended the equestrian extravaganza wearing near-identical cord dungarees in shades of forest green and chocolate brown.
Aside from their outfits, the pair also twinned with their mops of creamy blonde hair - adorable!
2/5
Matching in matcha green
Peter appeared to be an absolute hoot in 1984 as the pair rode in a carriage at the Royal Windsor Horse Show.
While the youngster stole the show with his cheeky antics, their matching green sweaters also deserve a special shout-out.
3/5
Twinning in tartan
Zara and Peter sweetly coordinated with their mother Princess Anne as they arrived in Scrabster, Scotland, for their annual summer holiday.
Dressed to impress, the royal trio donned vibrant tartan outfits, with Peter rocking a moss green kilt while Zara donned a taupe iteration with red and grey threads.
For an extra dose of 'matchy-matchy' the sibling duo also wore identical navy leather lace-up shoes.
4/5
Countryside clones
Princess Anne and her two children made a strong case for the humble waxed jacket as they braved the spring chill for the Windsor Horse Trials.
While Anne nailed country chic in a navy trench coat and a paisley print headscarf, Peter and Zara twinned in short bottle green jackets and trusty Wellington boots.
As for accessories, Peter rounded off his look with a caramel tartan flat cap, while Zara opted for a waterproof bucket hat.
5/5
A welly great time
Zara and Peter looked so sweet as they donned matching jeans, navy sweaters and Wellington boots during an outing in Wiltshire.
Outfits aside, the pair also adopted identical pensive gazes as they re-charged their batteries in the glorious sunshine.
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