Shania Twain is leaning on the shoulders of family and friends to help her through the breakup of her 14 year marriage to Robert "Mutt" Lange. But it turns out it was one of her friends who is accused of being the 'other woman' in Lange's alleged affair.

Marie-Anne Thiébaud was a longtime secretary and house manager at Twain's estate in Switzerland, and sources tell PEOPLE magazine that she was also a close confident to the country superstar. PEOPLE has found a photo of Thiébaud with Twain from 2006. (You can see it here.)

"Mutt and Marie-Anne left their spouses for each other and are still in a relationship," one source told the magazine, adding that Marie-Anne and her husband were very tight with Twain's whole family. "Their two families would vacation and spend holidays together . . . Shania considered Marie-Anne one of her best friends."

Lange defended himself to PEOPLE, calling the split simply a "growing apart" and denying the accusations of an affair. He married Twain in 1993 and is the father to their 6-year-old son, Eja.