Baby hopes for Queen's birthday
The Queen is celebrating her 89th birthday amid the prospect of sharing it with a new great-grandchild.
Royal fans are hoping the Duchess of Cambridge's second child - the Queen's fifth great-grandchild - will make an appearance to coincide with the monarch's birthday.
The Queen is spending the day privately at Windsor Castle where she has been staying for the past month for Easter Court. Neither she nor the Duke of Edinburgh has any official engagements listed.
Bookmakers Coral have cut the odds on the royal baby being delivered on April 21 to 10 to1 - now joint favourite with Saturday April 25, the reported due date.
Coral's John Hill said: "There's every chance it could happen if you believe the odds".
The arrival of a girl on the same day the monarch turns 89 would undoubtedly lead to speculation the princess would be called Elizabeth - the third favourite name at 6 to 1, after Alice at 4 to 7 and Charlotte at 5 to 1.
In honour of the Queen, the King's Troop Royal Horse Artillery - in full dress uniform - will ride their horses and gun carriages past Buckingham Palace at midday en route to Hyde Park to stage a 41 gun royal salute using six First World War-era 13-pounder Field Guns.
Before the King's Troop arrives in Hyde Park, the Band of the Royal Artillery will play a selection of celebratory music close to the firing position.
An hour later, the Honourable Artillery Company will fire a 62 gun royal salute from the riverbank at the Tower of London, overlooking HMS Belfast. Three L118 Ceremonial Light Guns, similar to those used operationally in recent years in Afghanistan, will be used to fire the salute across the River Thames.
Princess Elizabeth Alexandra Mary was born at 2.40am on April 21 1926 - the first child of the then Duke and Duchess of York - at 17 Bruton Street, the Mayfair home of her mother's parents, the Earl and Countess of Strathmore.
Elizabeth II is Head of State, the Armed Forces, the Commonwealth and the Church of England, and has been married to the Duke of Edinburgh for more than 67 years. She has four children, eight grandchildren and four great-grandchildren, with her fifth great-grandchild due any day.
She has been on the throne for more than 63 years and on September 9, she will overtake Victoria to become the longest reigning monarch in British history.
The Queen has two birthdays - her actual one on April 21 and her official one in June, which is celebrated with the Trooping the Colour parade.