The caption said: 'Happy Birthday to Archie Mountbatten-Windsor who is celebrating his first birthday today! Archie is The Queen's eighth great-grandchild.'
Royals including The Duke and Duchess of Cambridge and Prince Charles and Camilla also shared birthday wishes to Archie on Instagram.
A royal expert said Harry and Meghan plan to treat Archie to an 'organic, sugar-free cake', a splash around in their pool, and a video call with the Cambridge children as part of his birthday celebrations, while under lockdown in the US.
Archie Harrison Mountbatten-Windsor was born on May 6, 2019, at 5.26am, weighing 7lb 3oz.