The King received a hug from niece Zara Tindall when he braved the rain to visit the Royal Windsor Horse Show.
Charles made his third public visit of the week to tour the popular equestrian attraction, which was a firm favourite with his mother Queen Elizabeth II.
The late monarch was a passionate fan of the event staged on her doorstep close to Windsor Castle and would frequently be seen walking among the stalls dressed informally and wearing a headscarf.
Charles and his niece embraced and shared a few words when they met during the King’s first visit to the event as monarch.
The pair met overlooking the Royal Windsor Endurance course, in Windsor’s beautiful Great Park, which takes riders along landmarks such as the famous Long Walk.
The King later had tea with Salman bin Hamad bin Isa Al Khalifa, Crown Prince and Prime Minister of Bahrain which supports the Endurance event.
The day ended with the King taking his seat in the royal box with the Duke and Duchess of Edinburgh and receiving the applause of crowds, which he acknowledged with a wave.
Charles watched the Pony Club mounted games championship, a madcap event created by the late Prince Philip to test the riding skills of competitors, which left the King laughing and had the spectators cheering and shouting.
The head of state has attended a series of events since it was announced last Friday he would be returning to public-facing engagements, indicating the positive effect of his cancer treatment.
His first was a visit to a cancer treatment unit in London on Tuesday, where he met other cancer patients and spoke of his “shock” at receiving the diagnosis and told those who asked that he was “well”.
Buckingham Palace was the venue on Wednesday for the presentation of the Coronation Roll to the King and Queen, who marvelled at the document which recorded all the key events from their crowning last year.
Earlier on Friday, among the royal party were Lord Soames, a long-time friend of the King, who served as his equerry when Charles was the Prince of Wales, comic Rory Bremner, former racing driver Jackie Stewart and ex-defence secretary Ben Wallace.
Charles was also pictured chatting to Simon Brooks-Ward, director of the Royal Windsor Horse Show, who knew the late Queen well.