Zara Phillips, the oldest granddaughter of Queen Elizabeth, is engaged to marry England rugby player Mike Tindall.
Buckingham Palace said Mr Tindall, 32, had proposed on Monday at the couple's Gloucestershire home.
Miss Phillips, 29, who is 12th in line to the throne, said she was "very happy".
She is the daughter of Princess Anne and her first husband Mark Phillips.
No wedding date has yet been set.
The BBC reports Miss Phillips and Mr Tindall met during the Rugby World Cup in Australia in 2003, which England won.
She has achieved sporting success in her own right, winning individual gold in three-day eventing at the World Equestrian Games in Germany in 2006.
The title helped her become BBC Sports Personality of the Year later that year. Princess Anne won the award in 1971.
Tindall has played more than 60 times for England.
Princess Anne rode in the 1976 Olympics and was European champion in 1971, while Mark Phillips won an Olympic team gold in eventing in 1972. They divorced in 1992.