Princess Eugenie Shares Never-Before-Seen Footage of Her Son on IG

Princess Eugenie's son, August Brooksbank, just turned four years old, and she's marking the occasion with a special Instagram tribute.

On her official account, the royal, who shares August with her husband, Jack Brooksbank, shared a sweet montage that includes rare photos and video footage of the preschooler. She wrote, "Happy birthday my darling Augie. Four today. And what an amazing 4 years. 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. I love you my boy, my angel."

The proud mom offered glimpses of August holding his "4" shaped birthday balloon and spending quality time with the family. But the moment that stood out most? His playdate with a mystery friend.

In the montage, there's a brief clip of August walking through the park, decked out in a navy puffer coat with jeans. He's also walking hand-in-hand with a young girl who's sporting a fluffy pink jacket. And some fans suspect that it's his cousin, Sienna, the 3-year-old daughter of Princess Beatrice and Edoardo Mapelli Mozzi. Since their faces are hidden, it's quite hard to tell. But considering the tight-knit bond between Princess Eugenie and her sister, it would make total sense that their kids are just as close.

In the comments, one fan wrote, "Wishing your lovely August a very Happy fun Birthday. Such great photos of your fabulous family." Another called out August's resemblance to his dad and wrote, "He looks like his father. Happy Birthday from me."