The Duke of Edinburgh is celebrating his 94th birthday as he spends the day privately with his diary free of public engagements.

Philip last night joined the Queen, the Prince of Wales and Prince Harry at the Gurkha 200 Pageant at the Royal Hospital Chelsea to mark two centuries of unbroken Gurkha service to the crown.

He is expected to mark his birthday at Buckingham Palace with the Queen, who has audiences to carry out but no official appearances.

The royal couple, who married in 1947, are due to celebrate their 68th wedding anniversary later this year.

June is always a busy time for the royals. The Duke is due to attend Trooping the Colour - the Queen's annual birthday parade - with the monarch on Saturday, followed by Monday's national commemoration to mark the 800th anniversary of the sealing of Magna Carta at Runnymede Meadows in Surrey, and then the Order of the Garter service back at Windsor.

Next week will see Philip head to Royal Ascot for the annual racing meet and, at the end of the month, he will accompany the Queen on a four-day state visit to Germany, where they will be shown the site of the Bergen-Belsen Second World War prisoner of war and concentration camps.

Gun salutes will be fired to mark Philip's birthday.

The King's Troop Royal Horse Artillery will ride past the Palace en route to Green Park to stage a 41-gun royal salute at midday using six First World War-era 13-pounder field guns.

At 1pm, the Honourable Artillery Company, the City of London's Reserve Army Regiment, having driven their liveried Pinzgauer all-terrain military vehicles from their barracks at Armoury House to the Tower of London, will fire a 62-gun salute across the River Thames, using three L118 ceremonial light guns.

Prince Philip of Greece and Denmark was born on the island of Corfu on June 10 1921 to Prince Andrew of Greece and Princess Alice of Battenberg.

His early years were marked by upheaval after the family went into exile following a military coup in Greece which overthrew Philip's uncle, King Constantine I.

He moved to England to stay with relatives and study at Cheam Prep School in 1928, before spending a year at Salem School in south Germany, then finally enrolling at Gordonstoun School in Morayshire.

Philip went on to join the Royal Navy and, while a cadet, he caught the eye of a 13-year-old Princess Elizabeth. He served with distinction during the Second World War and his friendship with the Princess grew into love.

They married two years after the end of the war. Within f ive years, George VI had died and Princess Elizabeth had become Queen.

The Duke, who is known for his no-nonsense approach and acerbic wit, is the longest serving consort in British history and also the oldest serving partner of a reigning monarch.