Robert "Mutt Lange offers a very simple explanation for his separation from his wife of 14 years, Shania Twain.

"It's just an unfortunate thing that's happened," Lange tells PEOPLE magazine. "It's literally just a growing apart, that's all."

An unnamed source close to Twain also tells PEOPLE that the singer didn't expect the split. "She's devastated," the source says. "She's getting through it with a very close-knit group of family and friends."

Twain and Lange were married in 1993. They have a 6-year-old son, Eja.