Duchess' 'slip' prompts speculation royal baby is a girl

London (CNN) -- British newspapers are abuzz with speculation that Prince William's pregnant wife Catherine is expecting a girl after a member of the public reported hearing what seemed to be a hint that a daughter is on the way.

The Duchess of Cambridge was talking to people who turned out to welcome her as she visited the coastal town of Grimsby, in northeast England, on Tuesday when the apparent slip of the tongue was made.

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"The lady next to me gave her a teddy bear and I distinctly heard her say: 'Thank you, I will take that for my d...' Then she stopped herself," recounted Sandra Cook, 67.

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"I said to her: 'You were going to say daughter, weren't you?' She said: 'No, we don't know'. I said: 'Oh I think you do', to which she said: 'We're not telling'."

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Whatever Catherine, now five months pregnant, might have been meaning to say, the story has prompted a rash of headlines in UK newspapers.

"It's a girl! Pregnant Duchess of Cambridge drops huge hint she's having a daughter," proclaimed the Mirror.

"Has Kate just given the game away?" asked the Daily Mail.

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A royal source quashed the speculation, telling CNN that the duke and duchess don't yet know the sex of their baby.

Catherine, who was hospitalized with acute morning sickness in December, recently returned to public duties.

The baby, who will be a great-grandchild of Queen Elizabeth II, is due in July.

If the child does turn out to be a girl, she is destined to ascend the throne as queen one day.

Planned changes to the law of succession that end the tradition of a boy taking precedence over an elder sister are already de facto in effect, the British Cabinet Office has said.

The child will be next in line to the British throne after William, whose father Charles is first in line.