It's a huge week for the King and Queen, with their historic US State Visit dominating headlines across the globe. Closer to home, however, there's another significant royal event being celebrated on a much more personal scale. Today (29 August), marks the 15 years anniversary of The Prince and Princess of Wales, and the couple marked the occasion by releasing a new and never-before-seen family portrait.

Taking to Instagram, Prince William and Kate shared a sunlit photograph of them lying on the grass alongside their three children; Prince George, Princess Charlotte and Prince Louis. The family are smiling and relaxed, looking joyful and at peace together in nature. Alongside the image, they included a simple message saying they were, 'celebrating 15 years of marriage', which makes today their crystal anniversary.

The Royal Family's love of the outdoors is no secret, and the Princess of Wales in particular has stressed her emphasis on spending time in nature with her children, especially when they're away from the public eye. Many of their family portraits - whether together or individual - tend to be taken in natural settings.

Just last week, for example, the couple marked their youngest son's eighth birthday with a brand new portrait of Prince Louis against an ocean backdrop, alongside a video montage.

Other portraits have seen the family playing in the sand together, sitting in a meadow of daffodils and a notable Christmas card image even featured them in the red desert, taken while on a private holiday in Jordan.