The Queen has fondly remembered becoming the first young person in the Commonwealth to receive a junior lifesaving award from the Royal Life Saving Society.
As Princess Elizabeth, she was 14 years old when she earned the junior respiration award in February 1941.
Her Majesty, 95, learnt she was the very first to receive the award during a call last week with the society.
When told 80 years had since passed, she proclaimed: "That's terrible!"
The Queen smiled and looked in good spirits during last Thursday's virtual meeting, just days after she began official engagements following the death of her husband, the Duke of Edinburgh.
It comes as she prepares to carry out her first major public ceremonial duty since Prince Philip's death in April, when she attends a scaled-back and Covid-secure state opening of Parliament on Tuesday.
The fact she was the first young person to receive that particular award appeared to have been news to the monarch, who responded with surprise during the call with the society.
She said: "I didn't realise I was the first one. I just did it, and had to work very hard for it. It's a very long time ago, I'm afraid, I think it's changed a lot."
Clive Holland, deputy Commonwealth president of the society, told her: "Your Majesty, when you say it was a long time ago, it was in fact 80 years ago."
The monarch also met Sarah Downs, a 20-year-old student who saved a child's life when she was on duty as a lifeguard at a swimming pool in Exeter in 2018.
Ms Downs asked the Queen about her experience of qualifying as a junior lifesaver, training for which took place at a private members' club in Mayfair, central London.
The Queen said: "Well, it's a very long time ago. I do remember it was of course all done in the Bath Club in the swimming pool.
"And I suppose I didn't really actually realise quite what I was doing, you know, because I think I must have been 12 or something, 12 or 14, or something like that.
"But it was a great achievement and I was very proud to wear the badge on the front of my swimming suit. It was very grand I thought."
Ms Downs, a physiotherapy student at Manchester Metropolitan University, won the society's Russell Medal for resuscitating a boy at the Middlemoor Pool in Exeter.
The Russell Medal is awarded annually to someone under 18 for displaying bravery and quick-thinking under pressure.
Ms Downs said that a boy had a fit underwater as she was getting some arm bands.
She added: "So when I came back to the shallow end, being notified of this child under the water and then getting him out of the pool, I completed CPR (cardiopulmonary resuscitation) on him to resuscitate and bring him back around."
The monarch also praised the bravery of another young lifesaver, Tanner Gorille, from Cape Town, South Africa, and congratulated Dr Stephen Beerman, from Canada, for his outstanding contributions to the prevention of drownings.
The Queen is patron of the Royal Life Saving Society, which was founded in London in 1891.