Brit Didn't Know Sis Was Preggers.

Britney Spears only discovered her teenage sister was expecting her first child on Tuesday, 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 was 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.