On a visit to Belfast, she said the monarch was "doing very well" as he receives treatment for cancer.

It came on the day a new picture of the King was published showing him in a car being driven out of Clarence House.

The Queen, who is travelling without her husband after he stepped back from public duties, was handed a get well card for him at a delicatessen, where she also visited a butcher's and a bakery.

She thanked shop assistant Brenda Robb, who gave her the card, along with her best wishes, and told her the King was "doing very well" and that he was "very disappointed he couldn't come".

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Ms Robb said of Queen Camilla: "She was beautiful, a real lady. She accepted a get well card that I got for her husband and she said she was sorry her husband wasn't here.

"It was a very appropriate card. It had a wee saying from Belfast, basically rest up, take care, and on the back of it, it said from Ireland. It was picked with love.

"People say maybe he'll not get the card, but I think he will."

The monarch is being treated for a form of cancer at the London Clinic, an exclusive hospital - frequently used by members of the Royal Family - in central London, where Kate, the Princess of Wales, underwent abdominal surgery earlier this year.

Buckingham Palace has not revealed what type of cancer he is being treated for.

The Queen had been in south Belfast where she stopped at Coffey's Butchers, The Arcadia deli and Knotts Bakery before doing an impromptu meet and greet with well-wishers.

She was presented with a gift of some local favourites at Coffey's, including vegetable rolls and beer sausages, and responded by saying: "I shall take these back for my husband, he will make the most of them."

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At Knotts, Camilla met owner William Corrie, as well as his wife, former Miss Northern Ireland and Blue Peter presenter Zoe Salmon, and their one-year-old son Fitz.

The Queen smiled and chuckled as a joke was made about the young boy, dressed in a tuxedo, stealing her thunder.

She left Knotts with a gift of a fruit loaf and some iced madeira cake, adding she hoped to snack on it later.

The royal met Northern Ireland's First Minister Michelle O'Neill and deputy first minister Emma Little-Pengelly, as well as authors, actors and performers at an event highlighting the importance of literature and World Poetry Day at Hillsborough Castle.