Another Spears baby is reportedly on the way - and it's not Britney's.

Jamie Lynn Spears, the 16-year-old star of Nickelodeon's "Zoey 101" and kid sister of Britney, told OK! magazine that she is pregnant and that the father is her boyfriend, Casey Aldridge.

"It was a shock for both of us, so unexpected," said Spears, who is 12 weeks along.

After going to a doctor, she said, "I took two weeks to myself where I didn't tell anybody."

She broke the news to her mother, Lynne, just before Thanksgiving, the magazine reported.

"She was very upset," Spears said, "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, already grandmother to Britney's two young sons, told the magazine: "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 plans to raise the baby in her home state of Louisiana - "so it can have a normal family life," she says.

Nickelodeon released a statement, saying in part: "We respect Jamie Lynn's decision to take responsibility in this sensitive and personal situation."