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, "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).