London- Britain's Queen Elizabeth II marked her 83rd birthday Tuesday with low-key private celebrations at Windsor Castle as gun salute tributes were fired in her honour and flags were flown above government buildings.

The monarch, who became queen on the death of her father, King George VI, in 1952, would spend the day quietly at Windsor Castle, just outside London, with her husband, 87-year-old Prince Philip, the palace said.

The queen, who is head of state, of the armed forces, the Commonwealth and the Church of England, has been married to Prince Philip for more than 61 years.

The Duke of Edinburgh reached his own milestone last week, when he became the longest serving consort in British history. The couple, who married in November, 1947, have four children and eight grandchildren.

The queen traditionally has two birthdays - her actual one on April 21 and her official one in June, which is celebrated with the Trooping the Colour parade. (dpa)