The Twilight proposed to the actress Monday on top of the Empire State Building.
The couple, met when they worked on the comedy-drama Nurse Jackie. They were first romantically-linked in November 2012.
“I know how [the relationship] makes me feel in my heart … it makes me feel really good. He’s a good guy with a great family and I couldn’t be any luckier,” Alexander told PEOPLE in November 2012.
The couple have yet to reveal a wedding date.