Later, Princess Beatrice was seen to give a small chuckle as the Dean of Windsor said of her grandfather: “He could be somewhat sharp in pricking what he thought to be bubbles of pomposity or sycophancy.”

As the congregation sang God Save The Queen, seeming to stand an inch taller for the now rare rendition in the presence of the monarch herself, the Queen seemed moved and blinked rapidly in an unusual break with total composure.

As she departed, walking back the way she came, she flashed a broad smile at Doyin Sonibare, the DofE Gold Award holder who read her own tribute and who had been escorted to meet her.

Ms Sonibare, 28, said: “She thanked me for my speech. She was lovely, really kind. And she asked what I did for my Duke of Edinburgh award.”

Confirmation of the Queen’s attendance was left until just hours before her arrival as aides waited to learn how she was feeling.

In the event, no casual onlooker would have realised there was anything amiss.

Her appearance has raised hopes that she may be able to take a slightly more active part in her Jubilee celebrations in June.

Palace sources have indicated that she will pace her diary accordingly, intended to join in the key events of the bank holiday weekend in some form.

On Tuesday night, the Royal family hosted receptions for visiting foreign royals.

The Prince of Wales entertained the kings, queens, crown princes and princesses at Clarence House, while relatives of the Duke were welcomed to Windsor by the Queen. Prince Charles is understood to have joined the family reunion later along with his siblings.