The couple, both 28, will get married next year, according to US Weekly. Sources tell the magazine they do not plan to announce their engagement until next year as well.
A palace rep would not confirm the engagement, saying they do not comment on the couple's privates lives.
The report is just the latest in a long line of stories speculating on when, or if, the couple would get married. British tabloids such as News of the World reported that a royal wedding date was set for 2012. The date was scheduled to coincide with the 60th anniversary of the accession of his grandmother, Queen Elizabeth II, and the 2012 Summer Olympics, which will be held in London.