Britain's Prince Andrew (L), Prince Harry (2nd L), Prince William (R) and Catherine, Duchess of Cambridge stand on the balcony of Buckingham Palace after the Trooping the Colour ceremony in central London June 15, 2013.[Photo/Agencies]

Britain's Duchess of Cambridge, Kate Middleton, will give birth to the future heir to the British throne in the same hospital where the late Princess Diana gave birth to Princes William and Harry, royal sources said on Wednesday.

The new royal baby, who will become third in line to the throne behind grandfather Prince Charles and father Prince William, will be born in the private Lindo wing of St Mary's Hospital in Paddington, West London.

The sources said the royal couple have still not been told the sex of the baby which is due next month as they want it to be a surprise.

However speculation about the baby's sex has swirled since March when the duchess accepted a teddy saying: "Thank you, I'll take this for my d.."

Bookmaker William Hill said this dropped "d" led to such wide speculation that the baby was a girl that it suspended all bets on gender just weeks later while rival bookmaker Paddy Power paid out on bets that it was girl.

The birth will be announced in the traditional way, the sources added, with an envelope containing notice of the baby's details taken from the hospital to Queen Elizabeth's London residence, Buckingham Palace, where the news will be posted on the main palace gates.

The baby will be delivered by Marcus Setchell, the Queen's former gynecologist.

Princess Diana, who died in a Paris car crash in 1997, gave birth to William in 1982 and to his younger brother Harry - who will drop a place in the line of succession after next month's arrival - in 1984 at St Mary's.

William, 30, and Kate, 31, married in April 2011, taking the official titles the Duke and Duchess of Cambridge, and announced they were expecting a baby in December last year.

Bookmakers said bets on names were rolling in from over 100 countries with Alexandra the clear favorite followed by Diana and then Elizabeth.

Alexandra has a history in the royal family with Princess Alexandra, 76, a cousin of Queen Elizabeth and Queen Victoria's son Edward VII married to Alexandra of Denmark in 1863.

The favorite boy's name is George and the favored date for the birth is July 17.

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