Princess Beatrice's daughter Sienna's first steps caught on camera in rare family video

Princess Eugenie lit up Instagram on Sunday when she shared a rare montage of unseen family photographs and videos to mark her son, August Brooksbank, turning four.

The mother-of-two, who shares 'Augie' and Ernest, 22 months, with her husband Jack Brooksbank, delighted her 1.8 million followers when she shared the sweet clip. Take a look below…

"Happy birthday my darling Augie. 4 today. And what an amazing 4 years," the Princess began.

"You are so incredibly focused and inquisitive and full of adventure and speed. Can't wait for all our adventures...so many more to come."

Signing off the sweet post, Eugenie added: "I love you my boy, my angel."

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August's playdate with cousin Sienna

In the heartwarming video, royal fans noticed a clip of August holding hands with a young girl - presumably his cousin Sienna - who is the three-year-old daughter of Princess Beatrice and Edoardo Mapelli Mozzi.

The toddlers held hands and walked through a leafy green park. August looked super cute in denim jeans and a navy puffer jacket, whilst the little girl wore white jeans, chunky pink trainers and a fluffy pink hooded coat.

The sweet video marks the only time royal fans have seen Sienna walking, with Princess Beatrice choosing to keep her family largely out of the spotlight.

The royal cousins share a sweet bond

It's not the first time we've seen Princess Eugenie and Princess Beatrice's young families spending time together, which makes sense considering the sisters' extremely close relationship.

In April 2023, Eugenie shared a photograph of August and Sienna at London Zoo - and the royal tots looked like the best of friends. Both children were seen pressing their hands against a glass enclosure as they admired some penguins.

Sienna's strawberry blonde hair was on full display, and she wrapped up in a cream borg coat, pale chinos and black trainers. August, meanwhile, looked cool in dark denim jeans and a beige coat with a white shearling collar.

Princess Eugenie and Princess Beatrice's sisterly bond

Eugenie previously shed light on her tight-knit relationship with her older sister during an episode of the White Wine Question Time podcast in 2023.

"Beatrice and I, our whole lives, we've always had each other," Eugenie began, which explains why raising their children together was always a given.

"We're the only ones going through exactly what the other is going through at exactly that time as a girl – in our family, our place of work, whatever it is. I think that's extraordinary to think about."

She added: "We're not twins, yet you go through life knowing exactly what the other one is going through. She's my big sissy, she's a legend."