In fact, here in Britain, the news hit us like a bombshell. Like his wife, Prince Philip looked like he'd just go motoring on forever.
That's partly the nature of monarchy. The royal family becomes the eternal background to your life -- particularly if, like the Queen, the monarch has been on the throne for 65 years, longer than most Britons have been alive.
It's also because Prince Philip is so extraordinarily fit and energetic. I met him 18 months ago at lunch, at the Cavalry and Guards Club on Piccadilly in London. I was blown away by his youthfulness and mischievous wit.
The lunch was for the Gallipoli Association, to commemorate the centenary of the doomed Gallipoli campaign in 1915 -- when Winston Churchill tried, and disastrously failed, to win the First World War by sending Allied troops up the Dardanelles.
In the flesh, the prince is surprisingly small. There isn't a spare inch of fat on him -- he has the physique and the gait of a man 50 years younger.
He is extremely confident. Before lunch, he prowled at will around the reception room, free from the assistants who are usually on hand with members of the royal family. And he seemed entirely approachable -- so I approached him. I was prepared to follow the protocol on these occasions -- to address him as Your Royal Highness and bow my head.
But he immediately cast aside any expectations of deference, saying to me, "Who roped you into this?"
In an instant, my nerves and sycophancy disappeared. That sort of informal, teasing, conspiratorial opening line made it much easier to explain why I was at the lunch -- my great-grandfather had been killed at Gallipoli a century earlier.
I told him how my great-grandfather's last words to his second-in-command, who ducked down to avoid the Turkish gunfire: "Please don't duck, Fred. It won't help you and it's no good for the men's morale."
Fred lived for another 60 years. My great-grandfather was killed seconds later.
I asked Prince Philip what the rules were on ducking in the navy during the war, when he served with distinction.
"What a silly thing to do!" he said. "Not much point in ducking on a ship."
In that moment, I suddenly realized the truth about Prince Philip's "gaffes" -- the countless instances of supposed rudeness to members of the public in his 65 years of royal duties. He has declared, "British women can't cook"; said of the house belonging to his son, Prince Andrew, "It looks like a tart's bedroom"; and, to a Scottish driving instructor, "How do you keep the natives off the booze long enough to get them through the test?"
I could have pretended to have been offended by Prince Philip's remark about my dead great-grandfather. In fact, it was extremely funny and a great ice-breaker.
Suddenly, the wall of politeness and deference, that Prince Philip could naturally have built around him, came tumbling down. The "gaffes", I suddenly saw, were brilliant devices to make you feel at ease in his company. He was behaving like the sort of old friend who shows how much he likes you by teasing you.
I was lost in admiration for this great man: a war hero, a loyal royal consort and an extremely funny fellow. I hope he enjoys his retirement and keeps on amusing all those who come across him.