Ora, who releases her debut album at the end of the month, revealed her past love with 'Doo Wops and Hooligans' star Mars in an interview with German magazine Bravo.
"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," he told the publication.
Adding: "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 is also rumoured to have dated reality TV star Rob Kardashian and rapper Drake, whom she defended from his critics recently.
'Party (How We Do)', Rita's latest single, is expected to reach number one this weekend.
Photos: Rita Ora and more stars at T4 On The Beach 2012