German-American supermodel Heidi Klum and her bodyguard boyfriend Martin Kirsten have split after dating for a year and a half.

The 40-year-old made headlines in 2012 when she starting dating Kirsten, a few months after she filed for divorce from her former husband Seal. Their unusual relationship had drawn comparisons to Whitney Houston and Kevin Costner's 1992 film The Bodyguard - about a singer who falls for the man employed to protect her.

"Martin was there for her during a challenging time in her life and it was something she will always be grateful for," a friend close to Klum told People.

The two are also ending their professional relationship as well.

"They are no longer working together," another source told the publication. "Life is about timing. He was incredibly supportive and they were there for each other, but they're moving on now. They still have a great friendship."

The former Victoria's Secret star had previously praised Kirsten and revealed how he helped the supermodel's four children.

"This is one reason why I'm so fond of him ... He's been helping me for four years now, and he takes wonderful care of the kids. He plays with them, he protects them. I trust him," she told German magazine Bunte.

The Project Runway host had previously said she had changed since her separation from Seal.

"I don't think [I'll get married again] No. No," she said. "People say, 'Oh, God, how devastating to go through a divorce.' Did I wish for this to happen to my family? No. But everyone is healthy - we're moving on with our lives. It's not what I wanted - it's not what anyone wanted - but it's not a real problem."