Jason Derulo has revealed he is getting ready to propose to his girlfriend Jordin Sparks and has even written a song for when he pops the question.

The couple have been dating for over 18 months and the 'Don't Wanna Go Home' singer is getting ready to make Jordin is wife.

Jason, 23, has even written a song to accompany his proposal and he has a date in his mind when he is going to pop the question.

He is quoted by In Touch Weekly magazine as saying: "The proposal will be monumental. I wrote a song called 'Marry Me'. I have a date in mind. I want to surprise her but she's given me guidelines first. I have to ask her dad for permission."

Jordin has been very open about her relationship with Jason and has admitted she would love to settle down with him and start a family with the musician.

She previously said: "I hope to marry and have kids one day, for sure, and I do see him in my future. But we both have to be ready. If that happens one day, it will happen."

Jordin has also credited Jason with keeping her calm and stress free since they began their romance in August 2011. 

She said: "There is something as simple as him just being in the room with me that helps calm me down and makes me feel at ease ... He says sweet things. When you love somebody, the littlest thing can be the biggest thing."