Sofia Vergara and Heidi Klum ‘One-Upping’ Each Other With ‘Help From the Plastic Surgeon’

Sofía Vergara and Heidi Klum are all smiles for the cameras, but sources exclusively tell Life & Style there's a big-time rivalry behind the scenes as they each try to outdo one another — with not-so-subtle nip and tucks!

"There's a lot of pressure on both of them to be perfect, and as genetically blessed as they are, everyone's convinced they've been getting some help along the way from the plastic surgeon to stay so youthful," says a source.

The Modern Family alum, 52, and the German supermodel, 51, appear to be very friendly as judges on America's Got Talent , but off screen there's a competition of their own brewing.

"There's a very obvious game of one-upping being played between these two, but at least Sofía admits she gets some help," says the source. "Everyone just rolls their eyes at Heidi's claims about being totally natural."

Sofía is "actually quite open" about her changing body — "or at least to some extent, whereas Heidi's very guarded ," the source says. "She likes people to think she's totally natural and just happens to have her own fountain of youth."

One part of Sofía and Heidi's beloved bodies that they each say is totally real is their chests.

In fact, the source says they both "take a lot of pride" in "their boobs, and they both insist they're all natural — but a lot of people question that, especially with Heidi because she seems to have suddenly gotten bustier out of nowhere."

Adds the insider, "She and Sofía are so competitive, it wouldn't shock anyone if Heidi did get a boob job just to try and keep up with Sofía's curves ."

As for their faces, "Sofía openly admits that she's been getting Botox on her face and neck for years to keep her skin smooth and tight," the source says. "But Heidi vehemently denies it, even though she's in her 50s and hardly has a line on her face and has been a sun worshipper for years. There's no doubt she looks fantastic, but it's very suspicious to a lot of people that she's just not aging."

Earlier this year, a separate source told Life & Style that the Colombian actress' eating habits are grossing out her calorie-counting costar.

Sofía is known for her curves and her love of digging into a plate of pasta, while the model sticks to a pared-down diet to maintain her fit figure.

"They don't have much in common besides their jobs on America's Got Talent and don't share the same tastes in style, mannerisms and especially food! Heidi has dieted most of her life and she's strict about what goes into her body," the source said. "A meal for her is raw veggies and fruit, while Sofía loves to eat and makes a big show of it, almost like she's rubbing it in Heidi's face."

According to the source, the frenemies play nice in public, but everyone can see their relationship is forced. "They are civil and go online with plenty of showy selfies," said a show insider, "but that's as far as it goes."