Heidi Klum's relationship with her bodyguard is reportedly "hard to define."

The model and her musician partner Seal caused widespread shock when they announced their separation at the beginning of the year.

Their divorce is said to be stalling at the moment because Heidi and Seal can't agree on several annulment terms.

Heidi went on a family vacation to Sardinia recently accompanied by her bodyguard Martin Kristen.

Since the trip, there has been mass speculation that Heidi and Martin are dating.

"It's complicated," a friend told People magazine.

"Their relationship is hard to define."

Apparently Heidi really relies on Martin for emotional support as she moves forward in divorce proceedings.

"This has been a difficult time," the friend explained.

"Her inner circle of people she trusts is getting smaller and smaller and he is her No. 1 confidante."

Heidi and Seal are parents to four children together: Leni, eight, Henry, six, Johan, five, and Lou, two.