Heidi Klum And Martin Kirsten Split After Over A Year Of Dating

It's over for Heidi Klum and her bodyguard boyfriend.

The supermodel and her beau of a year and a half, Martin Kirsten, have split, People confirms. The couple, who began dating shortly after Klum ended things with ex-husband Seal in Jan. 2012, reportedly separated a few months ago. Klum, 40, and Kirsten, 41, are calling it quits on their professional relationship, as well.

"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 tells People.

Klum, who is a mother-of-four, gushed about Kirsten after they announced their romance, telling Bunte magazine, "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."

"Life is about timing. He was incredibly supportive and they were there for each other, but they're moving on now," another source explains. "They still have a great friendship."

UPDATE: Heidi Klum's rep confirmed the breakup to The Huffington Post, but had no further comment.