Ever since their father ascended to the throne in 2014, the duo, who are just two years apart in age, have flourished in the spotlight. And like many young royals - take your minds back to Princesses Eugenie and Beatrice and Princes William and Harry - they've done so in an array of matching outfits.
In his memoir, Spare, the Duke of Sussex explained how his mother's habit was "pure agony" for Prince William.
"Willy always hated it when anyone made the mistake of thinking of us as a package deal. He loathed it when mummy dressed us in the same outfits," he said. "I barely took notice. I didn't care about clothes, mine or anyone else's… But for Willy it was pure agony to wear the same blazer, the same tight shorts, as me."
You may also like
Keep scrolling to discover some of Leonor and Sofia's cutest twinning moments…
1/9
Matching trench coats
In 2019, Princess Leonor and Infanta Sofia donned matching trench coats as they paid a visit to Asiegu, which had been honoured as the 2019 Best Asturian Village. During the visit, they paused to hug one another in a sweet display of sisterly affection. Adorable!
2/9
Precious in pink
The Easter service is a key date in the Spanish royal family's calendar - and 2010's celebration was certainly no exception.
For the special occasion held at Palma de Mallorca Cathedral, royal tots Leonor and Sofia melted hearts in matching bubblegum pink peacoats, scalloped white socks and matching white Mary Jane shoes.
3/9
Summer twins
Leonor and Sofia looked so sweet in August 2014 as they stepped out wearing matching cotton summer dresses.
Whilst eldest Leonor opted for a sky blue colourway, little Sofia was dressed in a flamingo pink iteration. For an added matching element, the youngsters also wore their blonde hair in twinning side parts.
4/9
Angelic in white
In 2009, Princess Leonor and Sofia rocked matching white summer dresses and white leather sandals as they attended a concert on the third day of the 28th Copa del Rey Audi Sailing Cup in Palma de Mallorca.
5/9
Football fans
Mini football fans Leonor and Sofia could be seen wearing matching red football jerseys as they posed next to the UEFA EURO 2012 trophy following Spain's victory in the tournament. Aside from their tops, the sister duo also rocked matching plaits.
6/9
Coronation chic
For their father King Felipe's majestic coronation on 19 June 2014, sisters Leonor and Sofia wore matching brocade dresses in shades of blush pink and duck egg blue. Youngest Sofia completed her regal look with a sparkling dragonfly headband.
7/9
Easter charm
On 12 April 2009, Leonor and Sofia twinned in the most adorable vintage-style floral dresses in varying shades of blue.
The duo also rocked periwinkle blue knitted bolero cardigans, latte-hued tights and caramel Mary Jane shoes. Teeny blue ribbons were added to their golden locks for added Easter cheer.
8/9
Purple Princesses
Doting mother Queen Letizia dressed her daughters in precious summer dresses complete with delicate lilac flowers back in 2009 as they attended the 28th Copa del Rey Audi Sailing Cup.
9/9
Flower power
The duo twinned once again in August 2009 as they joined their parents in Palma during the summer holidays. They looked like butter wouldn't melt dressed in their cerise-hued dresses emblazoned with tiny roses.
Sign up to HELLO! Daily for all the latest and best royal coverage
By entering your details, you are agreeing to HELLO! Magazine User Data Protection Policy. You can unsubscribe at any time. For more information please click here.