The on-off couple, who have been dating for five years, have reportedly parted ways because hectic work schedules have left little time for their relationship, reports The Sun.
A source said that the pair struggled to find time for one another with Lewis being based in Switzerland, and said that their jobs "cost their relationship."
This news comes just a week after Formula One racing driver Lewis reportedly hinted that he was ready to settle down with singer and X Factor judge Nicole.
Lewis had implied he intended to marry Nicole, suggesting that he wanted to propose "before" they reached their sixth anniversary.
Nicole and Lewis met at the MTV Europe Awards in Munich in 2007 but briefly split in 2010. They reconciled in 2011, before splitting again but got back together January last year.
Reveal have contacted their reps for comment.
Kim Kardashian, Alesha Dixon & TOWIE: top stories of June in pictures -
Copyright: Twitter Kim Kardashian