Queen Elizabeth II on her birthday. On April 21, which would have marked the late monarch's 97th birthday, Prince William and Kate Middleton have released a never-before-seen image of the queen taken by the Princess of Wales last summer at Balmoral Castle in Scotland. In the photograph, Queen Elizabeth is seated on a green couch and surrounded by several of her grandchildren and great grandchildren, including Prince George, Princess Charlotte and Prince Louis. Also pictured are Prince Edward's children, James, Earl of Wessex, and Lady Louise Windsor, along with Princess Anne's grandchildren, who do not have royal titles: Savannah Phillips, Isla Phillips, Mia Tindall, Lena Tindall, and Lucas Tindall. A post shared by The Prince and Princess of Wales (@princeandprincessofwales)The new post comes just weeks before King Charles III's historic, star-studded coronation ceremony is set to commence May 6. Last month, the king honored his late mother with another throwback image on his first U.K.