1. Elizabeth Alexandra Mary was born at 2.40am on 21 April, 1926, at 17 Bruton St, Mayfair, London.

2. She also has an official birthday in June - this year it falls on Saturday 11 June.

3. She was born by caesarean section - described at the time in a statement by royal doctors as "a certain line of treatment".

4. The then home secretary, Sir William Joynson-Hicks, was waiting in a nearby room throughout the labour. The now dispensed with custom made sure the new arrival was a genuine descendant of the monarch and not an imposter who had been smuggled in.

5.  She was named after her mother, while her two middle names are those of her paternal great-grandmother, Queen Alexandra, and paternal grandmother, Queen Mary.

6. She was christened on 29 May, 1926, in the private chapel at Buckingham Palace.