She cared for them for many years through their parents' divorce and the death of their mother Princess Diana.
So Princes William and Harry were hugely upset to hear that Olga Powell had died of a heart attack.
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A spokesman said: "The Princes have been informed and are very saddened to hear the news."
Olga, an 82-year-old widow collapsed on her doorstep this week.
For 15 years at Kensington Palace she was a kindly presence, dispensing hugs and, if need be, a firm word of rebuke.
Her reward was that the boys regarded her as family and their old nanny was invited to the royal wedding last year.
Watch: Prince William takes George to meet his sister
It's a little princess!