Mary Edmondson, 89, was delighted to be presented with a basket of flowers by Charles following the service at Canisbay Parish Church in Caithness on Sunday.
Charles, known as the Duke of Rothsay in Scotland, was staying at the Castle of Mey near John O’Groats, which belonged to the late Queen Mother, and like her attends Canisbay Parish Church when he is staying there.
Miss Edmondson began playing the organ at the age of 14 and has played the instrument in various churches across the past seven-and-a-half decades.
Charles congratulated her on her dedication and also delivered a letter from the Moderator of the General Assembly of the Church of Scotland, the Rt Rev Dr Iain Greenshields, who described her as “truly inspirational”.
Miss Edmondson was joined at the church service by her dog Poppy, who travels everywhere with her in a tartan carry basket.
Speaking after the service, the 89-year-old said Charles was “quite taken” by Poppy.
She said: “I go everywhere with her and I told her that she was going to meet the Prince and she licked his shoes, so that was nice.”
Charles was invited to make the presentation by the Rev Janet Easton-Berry.
She said: “Mary has been playing the organ in various churches and denominations for 75 years and started playing at Canisbay Church when she was 81.
“She is an amazing lady and much loved, so we wanted to organise a special surprise for her during the annual Royal Service.
“I told her at the last minute what was going to happen and the look of surprise on her face was wonderful because she did not have a clue.
“When His Royal Highness approached her with the basket of flowers and Moderator’s letter with a huge smile on his face she was in absolute shock.
“It was so lovely and very, very special.
“He is a very warm and gracious man and Mary held his hand and told him that she started playing the organ when she was 14.
“Prince Charles told her that she must be the most longstanding organist, having played for 75 years and still going.
“The presentation meant so much to Mary and I told her that we appreciated her and we loved her.”
After the service, Charles planted a rowan tree in the church garden to mark the Queen’s Platinum Jubilee and a plaque will be put up at a later date.