Britney Spears only discovered her teenage sister was expecting her first child on Tuesday (18Dec07), according to a family friend.

Jamie-Lynn, 16, confirmed she is 12 weeks pregnant with student Casey Aldridge's baby during an interview with OK! magazine.

But Spears found out about the pregnancy through a media outlet - although the rest of her family were informed at Thanksgiving.

A source tells People.com, "This is going to kill (Britney). In the end, she'll be supportive, but this is a big shock."

The baby is due in June (08). (LJ/WNWCPL/JC)

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