The garment has a sweet significance to Kate and Prince William as it was thought to be a gift from their nanny, Maria Teresa Turrion Borrallo.
While Princess Charlotte and Prince Louis reportedly wore the same item, eagle-eyed royal fans noticed it was styled differently.
Princess Charlotte sported it the opposite way to how it was designed whereas Prince Louis wore it the right way around.
Earlier this year, Kate opened up about posing for the photo calls while speaking on Giovanna Fletcher’s podcast, Happy Mum, Happy Baby.
The Duchess of Cambridge said: “Yeah, slightly terrifying, slightly terrifying, I’m not going to lie.