Jamie Lynn Spears, Britney's sister, is pregnant, the 16-year-old told OK! magazine. The father is her longtime boyfriend, Casey Aldridge, she said. "It was a shock for both of us, so unexpected," Jamie Lynn Spears, who is 12 weeks along in her pregnancy, told the magazine for its new issue, which hits stands this week.

"I was in complete and total shock, and so was he," she said. "As soon as I found out for sure from the doctor, I took two weeks to myself where I didn't tell anybody. Only one of my friends knew because I needed to work out what I would do for myself before I let anyone's opinion affect my decision. Then I told my parents and my friends. I was scared, but I had to do what was right for me."

According to the interview, Jamie Lynn confirmed the pregnancy through a home test. She later paid a visit to the doctor, who corroborated the news. She said she revealed the news to her parents shortly before Thanksgiving.

(Head here for fans' reactions to Jamie Lynn's pregnancy, and for an update on Lynne Spears' parenting book.)

Jamie Lynn said that her mother, Lynne Spears, "was very upset because it wasn't what she expected at all. A week after, she had time to cope with it and became very supportive." Lynne Spears also commented on the news, saying, "I didn't believe it because Jamie Lynn's always been so conscientious. She's never late for her curfew. I was in shock. I mean, this is my 16-year-old baby."

Jamie Lynn, a high school junior, reportedly plans to raise the baby in Louisiana, her home state, "so it can have a normal family life." In regards to the third season of her Nickelodeon show, "Zoey 101," which wraps January 4, Jamie Lynn said: "I haven't spoken to [Nickelodeon] personally, but they have always been so great to me over the past years and have given me so many opportunities." The show is slated to start back up again in February, and fourth-season filming is already done.

Nickelodeon issued a statement Tuesday afternoon, saying, "We respect Jamie Lynn's decision to take responsibility in this sensitive and personal situation. We know this is a very difficult time for her and her family, and our primary concern right now is for Jamie Lynn's well being."

When the magazine reportedly asked her about the message her pregnancy might send to young people, she replied, "I definitely don't think it's something you should do; it's better to wait. But I can't be judgmental because it's a position I put myself in."

Lynne Spears told OK! that her daughter had been dating Casey Aldridge for years. But in an Associated Press interview conducted shortly before Thanksgiving, Jamie Lynn said she did not have a steady boyfriend. "I kind of just keep my options open," she told AP. "I have a bunch of friends that I always hang out with, a bunch of guy friends." In the OK! interview, Jamie Lynn said she had met Aldridge at church.

Aldridge's mother, Joyce, spoke with TMZ about the pregnancy, saying, "We are aware of the recent interview regarding her and being pregnant, and we are in agreement with everything that was said by Jamie Lynn about the situation ... everything is fine. ... Casey will address all of this when it is time."

Also yet to be addressed is whether Jamie Lynn and Casey plan to marry. His uncle, Odus Jackson — who is a Baptist pastor — said in an interview with People outside his nephew's house in Mississippi, "They may or may not [get married]. You just never know." He added, "I hope they will stick it out and get married for the child's sake and their sake. But if they're not in love and it was just a fantasy, they don't need to make the same mistake twice."

According to a video posted on TMZ.com, Britney appeared not to be aware of the Jamie Lynn news before it broke wide, telling reporters during a shopping spree Tuesday night, "My sister's not pregnant!" But on Wednesday, the site ran a report in which a source said the singer was just being sarcastic.

What do you think about Jamie Lynn's news? Share your thoughts below.

[This story was originally published on 12.18.07 at 9:18 p.m. ET]