03/03/2013 AT 10:00 AM ET
She said yes!
“Guesssss what??????” Spears wrote, sharing a happy photo of the couple, left hand raised to show off the ring. “#Hedidgood.”
The singer and actress, 21, has been dating Watson, 30, on and off for three years, he told the New York Post in January.
Spears, the little sister of pop star Britney Spears – who recently ended her own engagement – was previously set to wed Casey Aldridge, the father of her 4½-year-old daughter Maddie. She and her little girl split their time between Nashville, Tenn. and Kentwood, La.