Gwendolyn Hoare's niece wrote about the surprise on the BBC's online tribute page to the Queen.
Gwendolyn Hoare, from Manningtree in Essex, thought her chances of receiving a 100th birthday card from Queen Elizabeth II were gone when the monarch died on 8 September.
But to her surprise one came through the post on Friday, a day before her birthday, making her one of the last people to receive a card from the Queen.
Gwendolyn's niece wrote about the surprise on the BBC's online tribute page to the Queen: "My Aunt, Gwendolyn Betty Hoare, is 100 today. For decades she talked about receiving a telegram from the Queen and was devastated to hear the news... but her telegram arrived and she was ecstatic."