Jamie Lynn Spears was an accident -- Jamie Spears had a vasectomy

Britney Spears' younger, pregnant sister, Jamie Lynn Spears was an accident, just like her unborn baby -- her uncle has claimed.

William Spears, the outspoken brother of dad Jamie Spears, who lives in a camper van, says Jamie was shocked when he found out his now ex-wife Lynne was pregnant as he had a vasectomy after she gave birth to Britney, their second child.

He said: "Jamie got awfully mad. He said it couldn't be his."

William claims that Jamie demanded a DNA test, that eventually proved he was the baby's biological father.

He added: "That's why they named her Jamie Lynn, to kind of make the point that she was from both of them."

Meanwhile, pop wreck Britney, 26, had another visit from her young sons Sean Preston and Jayden James yesterday -- her third in five days.

She spent spent three hours with the boys, after they were dropped off at her Beverly Hills mansion.

Britney's legal team are also reportedly trying to get visitation rights up to three times a week.