"Happy birthday to His Royal Highness The Prince of Wales - Sir, Pa, Grandpa!" read the caption, which was accompanied by a birthday cake emoji.
The photo was posted just ten minutes after Prince William and Kate Middleton took to Instagram to wish Charles a happy birthday.
The Duke and Duchess of Cambridge shared a series of sweet photos, including one of Charles with his grandson, Prince Louis.
"Wishing a very happy Birthday to The Prince of Wales!," they captioned the photos.
The royal is currently undertaking a two-day visit to New Delhi to strengthen the ties between India and the UK.
On Thursday, the 71-year-old royal met with representatives from the British Asian Trust, alongside American pop singer Katy Perry.
The Prince looked cheerful as he posed for several photos with the musician, despite him previously being photographed with painful and swollen-looking feet.
As part of his itinerary, Charles plans to cast a light on pertinent issues relating to climate change and the impact it is having on the nation.
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