ET has the latest...

Earlier this week, sources told People magazine that the surprising split between SHANIA TWAIN and her husband, producer ROBERT "MUTT" LANGE, was due to him having an affair with MARIE-ANN THIEBAUD, an employee at the couple's Swiss estate. Now the magazine has obtained photos of the woman in question.

"Their two families would vacation and spend holidays together," the source tells the mag. "Shania considered Marie-Anne one of her best friends."

Shania is reportedly back in her native Canada and friends say she is "devastated" and that "this came out of left field."

Meanwhile, when contacted by People, Lange denied the claim. "It's absolutely not the reason [for the separation]." Adding that he was not in romantic relationship with Thiebaud, he said, "I'm not, no. It's not true."