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Newly single Heidi Klum was recently seen enjoying some down time on the beach in Sardinia, Italy with her kids, her parents -- and a tall, dark and handsome man.

But Martin Kristen isn't a new guy in Heidi's life, per se.

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Kristen, who was photographed hugging the 39-year-old supermodel and playing with her children, has worked for Klum as a bodyguard for the past four years -- since long before she split from Seal.

"It's complicated," one of Klum's friends tels People. "Their relationship is hard to define."

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The insider adds that things have been "difficult" for Klum since she parted ways with Seal in January. "Her inner circle of people she trusts is getting smaller and smaller and he is her No. 1 confidante."

Right now, however, Klum's focused on herself. "I think everyone should work on their dreams," she told the mag last month. "I try to. I look into the future, concentrate on my family and I have to say that I'm happy. There are worse things in life than a separation."

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Klum and Seal, who were married for seven years, share four children: Leni, 8, Henry, 6½, Johan, 5½, and Lou, 2½.