After dating for a year and a half, a source tells People that the couple decided to call it quits a few weeks ago.
"Martin was there for her during a challenging time in her life and it was something she will always be grateful for," a source told the mag.
Klum, 40, began dating Kirsten, 41, a few months after her she filed for divorce from her husband of seven years, Seal.
"They are no longer working together," another source revealed.
"Life is about timing. He was incredibly supportive and they were there for each other, but they're moving on now," adds the source. "They still have a great friendship."