The 'Insatiable' singer and the NFL hunk announced their engagement last September but Nadine has revealed the pair decided to break up a few weeks ago after agreeing they were "better" as friends.
She tweeted: "A few weeks ago Jason and I broke up. We are great friends and decided we are better this way. I'm in NYC working & I love all your support. (sic)".
Nadine had previously predicted a long engagement for the couple, saying it could even last a decade.
She said: "It will definitely be a long engagement. We haven't even had an engagement party. I'm going to ride this one out. It still feels so new, so we could do this for ten or 12 years, you know!"
The news of the break up comes just after it was revealed Nadine and her Girls Aloud bandmates, Sarah Harding, Cheryl Cole, Nicola Roberts and Kimberley Walsh are to reunite next year for a tour.
Close pal Louis Walsh said: "I've been on the phone to Cheryl all day, honestly I can show you texts, she's fine. She's getting back with Girls Aloud in 2012 and they're going to tour."