William's uncle, Earl Spencer, described his joy at the new royal baby.
He said: "We're all so pleased: it's wonderful news."
The Earl, whose sister was the Duke's mother, Diana, Princess of Wales, added: "My father always told us how Diana was born on just such a blisteringly hot day, at Sandringham, in July 1961. It's another very happy summer's day, half a century on."
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Nick Clegg will attempt to win over the female electorate when he kicks off the Liberal Democrats' general election campaign later today.
Up to £140 billion of savings could be released when over 55-year-olds are allowed to cash in their pension pots from April 6th.
The party's plans include a £2.5 billion Time to Care fund for the NHS, capping rail fare increases and 3,000 more midwives.