Duke and Duchess of Cambridge have paid a heartfelt tribute to the Queen on the occasion of her 96th birthday.MORE: The Queen's poignant 96th birthday plans include a nod to the late Prince PhilipThe royal couple selected two touching photos to accompany their message, the first of which showed William and Kate with the monarch as they showed her round the Duchess's Back to Nature Garden at the 2019 Chelsea Flower Show. WATCH: The Queen's grandchildren and great-grandchildren lead the way at Easter serviceThe second image poignantly shows the Queen and her late husband Prince Philip posing with seven of their great-grandchildren.