Kate Middleton is wearing a diamond engagement ring after Prince William proposed to her on holiday in Kenya.
The royal, who had his girlfriend's father's approval, popped the question last month while the pair were away.
Having met eight years ago as students at St Andrews University, the couple have been photographed together on numerous occasions including on holiday, at William's RAF graduation ceremony and at a recent friend's wedding – which they arrived at together rather than attending separately, as is tradition.
David Cameron, who spoke to the prince before announcing the news in a cabinet meeting, said: "This is incredibly exciting news and I am sure the whole country will want to pass on their congratulations."
It is not yet known when exactly the couple will be marrying, but a statement from Clarence House confirms the event will be in the spring or summer of 2011.
Another public figure sporting a new diamond ring this week is Jessica Simpson, who admitted she was engaged after being photographed with the jewel on her ring finger.