The Queen is set to turn 90 on 21 April, her actual birthday - although she also gets to enjoy a second, official celebration in June.
Born in 1926 in London to the Duke and Duchess of York, later King George VI and Queen Elizabeth, the young Elizabeth Windsor was never destined to be Queen.
But when King Edward VIII abdicated in 1936, her father acceded to the throne - putting her in line to become the next monarch.
She has gone on to become the world's oldest reigning monarch, as well as the longest-reigning British monarch.
Test your knowledge about Queen Elizabeth II with our royal quiz...