The pair apparently met for a secret rendezvous at a London hotel, where they spent seven-and-a-half hours in each other's company.
Newspaper The Sun reports that the X Factor beauty and her former boyfriend – and his beloved dog Roscoe – were spotted arriving within minutes of each other.
It's thought Lewis had persuaded Nicole to take time out of her busy schedule so they could talk seriously about the possibility of giving their love another chance.
A source told the paper: "There’s something that keeps pulling them back together, it's as if they can't resist each other.
"They were determined to keep the meeting under wraps, which is why they chose a hotel that isn't used much by celebrities."
Nicole was giving nothing away about the outcome of their meeting as she arrived to film an X Factor special of Celebrity Juice on Wednesday evening.
She smiled demurely as she made her entrance in a skin-tight PVC dress which showed off her va-va-voom curves to perfection.