William is on leave from his duties as an air-sea rescue helicopter captain based at Anglesey, an island off the Welsh coast, as he prepares for the birth of his first child - who will be the future king or queen of England as the third in line to the throne.
The Duchess of Cambridge will give birth in the Lindo wing of St. Mary's Hospital in Paddington, central London, and has opted for a natural birth.
It is the same place Princess Diana gave birth to William and brother Harry.
Media from around the world is camping out with cameras outside the hospital in anticipation of the news, which will be first broken to Queen Elizabeth II by her grandson William on the phone.
Meanwhile, plans for a new commemorative coin were reviewed at the Privy Council on Wednesday and the Royal Mint confirmed it was part of its plans to mark the royal birth.
It will bring out a new 5 pound silver coin to mark the birth, bearing an iconic "St. George and Dragon" design.
The Royal Mint has already revealed plans to hand out a "lucky" silver penny to the parents of every baby born on the same day as the new prince or princess.
The Duke and Duchess of Cambridge do not know the gender of their baby, but bookies have taken a flurry of bets as punters make their own predictions.
Paddy Power claims we should expect a princess.
Alexandra is 6-4 favourite to be the chosen name for the new baby at Ladbrokes, with James 6-1 and George quoted at 10-1.
Experts believe the royal baby could trigger a near 250 pound million boost for the high street and stores across the country have already brought out commemorative products.