Prince William of Gloucester (William Henry Andrew Frederick; 18 December 1941 - 28 August 1972) was a member of the British royal family, a grandson of George V.

Prince William was born at Barnet, Hertfordshire. His father was Prince Henry, Duke of Gloucester (1900-1974), the third eldest son of King George V and Queen Mary. His mother was Princess Alice, Duchess of Gloucester (1901-2004), the third daughter of the 7th Duke of Buccleuch. As a grandson of the British monarch in the male line he was styled Prince of the United Kingdom of Great Britain and Northern Ireland with the style His Royal Highness.

He was baptised in the Private Chapel at Windsor Castle and on 22 February 1942 by Cosmo Gordon Lang, Archbishop of Canterbury. His godparents were: The King, Queen Mary, The Viscount Gort, Lord William Montagu-Douglas-Scott, Princess Helena Victoria of Schleswig-Holstein and Lady Margaret Hawkins.

In 1947, Prince William was one of his cousin The Princess Elizabeth's page boys (the other being Prince Michael of Kent) at her wedding to Philip, Duke of Edinburgh.

Prince William spent his early childhood at Barnwell Manor in Northamptonshire and later in Australia, where his father served as Governor-General from 1945 to 1947. He received his education at Wellesley House Preparatory School, Broadstairs, Kent, and at Eton College. After leaving Eton in 1960, he went to Magdalene College, Cambridge to read history, earning himself a BA. Subsequently, he was awarded an MA (Cantab.) in 1968.

In 1953, Prince William attended the coronation of his cousin, Elizabeth II.

After graduating in 1963, he spent a post-baccalaureate year at Stanford University studying political science, American history, and business. Upon returning to Britain, he took a position with Lazards, a merchant bank.

Prince William was the second member of the British Royal Family to work in the civil service or the diplomatic service (the first was his late uncle, Prince George, Duke of Kent in the 1920s). He joined the Foreign and Commonwealth Office in 1965 and was posted to Lagos as the third secretary to the British High Commission. In 1968, he transferred to Tokyo to accept the post of second secretary (commercial) in the British Embassy. In 1970, the Duke of Gloucester's health began to fail and he was diagnosed as suffering from porphyria. Prince William resigned from the diplomatic service and returned to Britain. For the next two years, he managed Barnwell Manor and began to carry out public duties as a member of the royal family.

Prince William served on some occasions as Counsellor of State in the absence of his cousin, the Queen.

A certified pilot, he owned several aircraft and competed in several air shows. He died when the plane he was piloting crashed at Halfpenny Green, near Wolverhampton. He was buried at Frogmore Royal Burial Ground. The comprehensive school in Oundle, which he opened in 1971, was renamed Prince William School in his memory.

Prince William was the heir-apparent of his father's peerages, Duke of Gloucester, Earl of Ulster, and Baron Culloden. Upon his death, his younger brother Prince Richard of Gloucester became heir-apparent and succeeded to these peerages in 1974.

*18 December 1941–28 August 1972: His Royal Highness Prince William of Gloucester

*Counsellor of State, 1962-1971

* British prince