Britney Spears' engagement may have been called off, but another Spears sibling is about to walk down the aisle.

Brit's younger sister, Jamie Lynn Spears, is engaged to her 30-year-old boyfriend of three years Jamie Watson!

The 21-year-old announced the news on her Twitter page on Saturday night, tweeting "Guesssss what??????" along with a photo of the couple, Jamie Lynn proudly showing off her ring.

Spears followed it up with a closeup shot of the sparkler ... and she clearly loves it. She tweeted "#hedidgood" along with the pic.

This will be the first marriage for Jamie Lynn, who was previously engaged to Casey Aldridge until they split in 2010. Casey is the father of Spears' daughter, Maddie.

Congrats to the happy couple!

UPDATE: Britney has sent her congratulations to her sis on Twitter, posting "So excited and happy for my sister, congrats @jamielynnspears - love you.