Oct 10, 2008, 9:40 GMT
Lynne Spears thought Jamie Lynn Spears was a virgin before she told her she was pregnant.
Lynne - mother of both Jamie Lynn and pop princess Britney Spears - believed her daughter was playing a prank on her when she said she was going to have a baby.
She told US TV programme 'The Morning Show with Mike and Juliet': "I thought she was joking when she first told me. I was looking at her face trying to wait for the punch line; wait for her to smile or joke.
"She wanted the baby from the beginning."
Lynne - who recently released a book documenting the lives of her showbiz daughters, 'Through the Storm' - also confirmed 'Zoey 101' star Jamie is still with her fiance and the baby's father Casey Aldridge, despite rumours they had split.
Lynne - who labelled herself as her daughters' "cheerleader" and not a pushy parent - added: "She and the baby's father are on. You can't believe the media. I don't know why they do that."
Earlier this week, Jamie Lynn, 17, was rumoured to be pregnant with her second child, but a spokesperson for the star denied the claim.
She gave birth to daughter Maddie Briann in June.
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