London (CNN) -- Queen Elizabeth II is marking her 86th birthday Saturday privately at Windsor Castle, a palace spokesman said.
The Queen also has an official birthday in June, which will be celebrated publicly as part of events to mark the Diamond Jubilee.
The Royal Gibraltar Regiment fired a 62-gun salute for her real birthday at the Tower of London, Retired Lt. Col. Stuart Green said.
Hundreds of guests gathered for the salute, which included 21 guns for the Queen's birthday, 21 because it's a royal palace and 20 guns to show the City of London's loyalty to the monarch, Green said.
The regiment, usually based in Gibraltar, is currently in London for ceremonial duties including guarding Buckingham Palace and the Tower of London, he said.
A 41-gun salute in Hyde Park and a 21-gun salute in Windsor Great Park were also held to honor the Queen.
The salute in Hyde Park was performed by the King's Troop Royal Horse Artillery, using teams of galloping horses to pull six World War I-era guns into position. The 41 rounds were then fired at 10-second intervals, the Ministry of Defence said.
On her official birthday each June, the Queen and other members of the royal family attend the Trooping the Colour military parade in central London.
CNN's Bharati Naik and Laura Smith-Spark contributed to this report.