Britney's sister Jamie Lynn engaged at 21

Jamie Lynn Spears has announced her engagement to Jamie Watson, her boyfriend of three years.

The 21-year-old revealed the happy news to her followers on Twitter when she posted the links to two photos on her Instagram site, one with her new fiancé and another of the stunning diamond ring.

Referring to the ring, she wrote: "He did good!"

Fans were quick to respond with their messages of support for the actress, the younger sister of Britney Spears.

One admirer said of the ring: "This ring is amazing!! So so beautiful, obv has a good eye! Congratulations (sic)."

This is Jamie's second engagement, after her on/off relationship with Casey Aldridge, the father of her four-year-old daughter Maddie.

Her big news comes two months after Britney, 31, announced she had split from her fiancé of 13 months, Jason Trawick.

Her representative Jeff Raymond said at the time: "Britney Spears and Jason Trawick have mutually agreed to end their one-year engagement.

"As two mature adults, they came to the difficult decision to go their separate ways while continuing to remain friends."