Why does the Queen have two birthdays?

Last updated at 10:12
The Queen on 5 April 2013

The Queen celebrated her 87th birthday with her family at Windsor Castle on Sunday.

On Saturday she enjoyed her favourite hobby - horse-racing - with a visit to Newbury Racecourse.

Gun salutes will be fired in London at 12noon on Monday, because her birthday falls on a Sunday this year.

Every year the Queen celebrates her actual birthday on 21 April and her 'official' birthday on a Saturday in June.

Why does the Queen have two birthdays?

Past monarchs' official birthdays have often been held on a different day to their actual birthday.

The main reason is when their actual birthday is not in the summer.

Having the official birthday in summer time means there's a better chance of good weather for the king or queen's birthday parade, called Trooping the Colour.

This year the celebrations are happening on 15 June.