Prince William Kate Middleton Royal Baby
Prince William and Kate Middleton, the Duke and Duchess of Cambridge, will have their royal baby in July (Reuters)

Bookie William Hill has slashed its odds on Prince William and Kate Middleton's royal baby being called Mary, after a "mystery punter" in a top hat and tails put £100 down on the name being chosen by the Duke and Duchess of Cambridge.

The posh punter got 14/1, but his sizeable bet led to William Hill cutting its odds to 10/1.

"The mystery punter came into one of our shops in west London, in full Ascot fig with a top hat and tails. £100 is a huge bet for this market, where the average bet just £3 so we are a little nervous that a member of the party at Royal Ascot has let the possible name slip," said a William Hill spokesman.

Wills's heir is due to be born in July. William Hill has the baby's gender at 2/5 for female and 7/4 Male.

Favourite among the names is Alexandra at 5/2, followed by Charlotte at 5/1. The shortest boy's name is George at 12/1.

Rank outsiders include Wayne and Waynetta, at 250/1 and 500/1 respectively.

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