Britney Spears' mum started to chuckle when she first learned her 16-year-old daughter Jamie Lynn was pregnant - because she thought it was a joke.

Lynne Spears has revealed the teenage actress handed her a note and told her to read it alone in the bathroom of the family's home.

It was the first time Spears realised her little girl was having a baby with her boyfriend Casey Aldridge - but she initially refused to believe what she read.

In an interview on America's Today show on Wednesday (17Sep08), Spears said, "I thought it was a joke... I kept waiting for the punchline."

But the matriarch quickly realised it was no laughing matter when Aldridge refused to look at her as she came out of the bathroom.

She added, "I was just truly in shock and then I started to cry. And then she (Jamie Lynn) started consoling me at that point."

The youngest Spears revealed she was pregnant in an interview in December (08). Lynne Spears details the day she learned all about the pregnancy, as well as other family highs and lows, in her new book Through The Storm. (c) WENN