The model took to her Twitter to break the news to her fans, writing: “It's a sad Day but I wanted to share with you that David and I are no longer engaged. I love and respect him and wish him all the best.”
Kelly, 34, and David have just returned from a romantic break away in Mykonos, Greece.
They were engaged in June and at the time, Kelly admitted she was taken aback by the former Gladiators proposal.
She said: “I think it took both of us by surprise, to be honest, how quickly things have progressed.
“But I've never met a guy like David before and although it seems soon to be planning our wedding, there's nothing to wait for in my mind because at the moment everything's fantastic and there's no reason why it can't continue to be like that.”
David has yet to comment on the news.