"It's complicated," a friend of Klum's tells PEOPLE, explaining that Kirsten, also 39, is Klum's "no. 1 confidante."
Well, someone cue Whitney Houston's "I Will Always Love You" because it seems like Klum is singing a different tune: On Wednesday's episode of Katie Couric's new daytime talk show, Klum, 39, admits, "[Martin]'s a great man and recently we just got to know each other from a completely different side."
"He's been with our family for the last four years. He's cared for our four children and helped us tremendously," Klum also said during her Katie interview. "I trust him with my children's life."
And her happiness, too, apparently. "He was always her rock," says an insider. "While everything was crumbling in her personal life he was there for her."
In addition, "he shows real care and concern for her and her children," adds the Klum pal. "She relies on him. It's a little bit of cliché with The Bodyguard movie. I don't know what will happen in their lives."
Why They WorkAfter seeing photos of the model-mogul and the South African bodyguard on a recent beach vacation to Sardinia with Klum's family, the attraction between the pair isn't hard to figure out.
"Tall and handsome are very accurate words for him," says a source. "He can be funny and light but he's also very professional, which is why I'm really surprised" by the relationship.
Trained in private personal protection with weapons, "Martin takes his job very seriously," echoes another family source. "It's not like him to cross the line with a client. At the same time it's totally understandable. Martin is very loyal to Heidi. They had a friendship that turned romantic."
Splash News Online
"If there's someone around who knows your children and knows everything around you, it's pretty comfortable and easy to connect," says the Klum friend.
One person who wasn't thrilled with the news? Klum's estranged husband Seal, 49, who declared his dismay in a now infamous TMZ video in which he said he wished Klum "waited until we separated before deciding to fornicate with the help."
(He later apologized in a statement via his rep for insinuating Klum was unfaithful during their seven year marriage.)
"He's upset," says a source close to the singer, who only learned of the budding relationship when the rumors made headlines. "What really bothers Seal was this guy was a dear friend. They called each other 'brother.' He feels betrayed."
Moving OnThough they are not seeing eye-to-eye on their dating lives (Seal was spotted in Sardinia with a mystery brunette but despite reports "he's gone out with some women but nothing serious," says the Seal source), Klum and Seal are rumored to be heading to a settlement in their divorce.
"I cherish all of the great memories Seal and I created together over the years," Klum said in an exclusive statement to PEOPLE. "My priority has and continues to be protecting and providing for our children."
"Divorce is complicated," says the Klum friend. "They have four kids and they're going to try and keep it together for them. It looks like there could be a peace treaty soon."
Or as Klum put it: "Seal has moved on and so have I."
With reporting by PERNILLA CEDENHEIM, JENNIFER GARCIA and MICHELLE TAN