Britney Spears' 16-year-old sister Jamie Lynn Spears is engaged to her longtime boyfriend and unborn baby's father Casey Aldridge.

The star of US television's Zoey 101 has been spotted showing off a diamond band to friends and family around Louisiana and Mississippi.

'She's got an engagement ring. She's been showing it off, talking about it,' People quoted a source, as saying.

Jamie and her 18-year-old fiance are expecting their baby this summer.

Last year, mom-to-be Jamie sparked a nationwide debate after revealing her pregnancy.