Whats this song?help!?

I guessing it came out like a year ago maybe a little longer because thats when I first heard it, but anyways im not so sure of the lyrics but it was a girl sayin something like......." sumthin sumthin sumthin sumthin we'll be together sumthin sumthin together forever....I didnt really hear it that well but it was on a rap/hiphop/top hits radio station and it was a girl, and im not sure but i thought i hear a man signing it sounded like jay-z but im not sure of anything except its a girl singing the chorus, and the song is not by donna lewis, sting, ashley tisdale......the beat is sumthin like- na na na na na nat nat na na, na na na na nat na na na na.....ANY info is greatly appreciated and sorry for bad details