Christina Aguilera has announced that she is engaged to her boyfriend of three years Matthew Rutler, E! Online reports. The singer and "Voice" mentor posted on Twitter: "He asked and I said . . . ," with a photo of her hand flaunting a large diamond ring as she holds his hand with beach scenery behind them. The couple met on the set of Aguilera's 2010 film "Burlesque," where Rutler was working as a production assistant. Aguilera was previously married to music executive Jordan Bratman.