The 'R.I.P.' singer, who has been romantically linked to Drake and Rob Kardashian, was in a relationship with the 'Grenade' star before either of them became famous.
They apparently met after her record label hired Mars to write tracks for her debut album.
"It was love at first sight, such a great experience. We met in 2009. I was 18 and starting out at Roc Nation. Bruno was unknown back then too," Ora told German media, reports The Sun.
"He was a struggling songwriter hired to write songs for me. I thought, 'Wow, that's just the world's greatest guy!'
"Our time together was wonderful. But once we got famous, work got in the way. We ended it last year. But we remained close. And when we were together we were so happy."
Ora's new single 'How We Do (Party)' is on course to hit number one on the UK singles chart this week after it topped the midweek countdown.
Watch the video for 'How We Do (Party)' below: