Prince William and Kate Middleton attended the opening day of the London horticultural event, their first as a couple. A Kensington Palace spokesman said the couple had not attended before because of "diary issues".
They added: "This year the diary has worked out fine and especially in the Queen's 90th year, their Royal Highnesses were keen to join her."
Also in attendance at this year's show, whose theme was Health, Happiness and Horticulture, were Queen Elizabeth and Princess Anne. Prince Harry was also present, and has previously visited to inspect a garden specially created in honour of his charity Sentebale, which supports children suffering with HIV/AIDS in Lesotho.
The Duke and Duchess of Cambridge walked through an impressive 21-foot floral arch containing 10,000 pastel blooms which commemorates the Queen's 90th birthday.
The Duchess wore a recycled, vivid green Catherine Walker coat dress, according to Hello! She previously wore the frock back in 2014 on a royal tour of New Zealand and Australia. In Sydney, the Duchess wore the vibrant green outfit when assisting in planting an English oak tree at the National Arboretum.
One of the highlights for Kate and William was seeing a new flower, named in honour of their daughter, Princess Charlotte. The Princess Charlotte chrysanthemum is being entered for the Flower of the Year category. Also known as the Rossano Charlotte, it is characterised by its pink colour and green tips.
It's producer, Dutch company Deliflor is the world's biggest breeder of chrysanthemums. Following the birth of their daughter Princess Charlotte, the company celebrated the event by sending the duke and duchess a special bouquet of flowers.
William and Kate will tour the gardens and see displays including '5,000 poppies', an Australian tribute of remembrance for those who have fought for their country in wars.