05/29/2008 at 08:00 AM EDT
's close friend and longtime assistant is finally speaking out – and denying reports she's behind the singer's surprise split from her husband of 14 years, PEOPLE reports in its new issue.
Speaking for the first time since the news of the alleged affair became public, Marie-Anne Thiébaud, 37, told PEOPLE, "You cannot believe everything you read in the press." When asked directly if she had an affair with Twain's husband, music producer Robert "Mutt" Lange, she replied, "No."
That contradicts several sources close to the situation, who say Thiébaud and Lange left their spouses for each other and continue to maintain a romantic relationship. Twain, 42, and Lange, 59, who have a 6-year-old son, Eja, announced their separation
May 15. Since then, the "You're Still the One" singer – "devastated" by the revelations, according to sources – has sought refuge with family in her native Canada.
Thiébaud began working for the ultra-private couple after they moved to Switzerland in 2000, acting as their personal assistant, secretary and manager of their vast château. By all accounts, she became one of Twain's closest confidants. The two attended the 2006 Swiss Red Cross Ball together (PEOPLE's exclusive first photos
of Thiébaud showed the pair at the event, posing together and smiling).
"They celebrated holidays and birthdays together," says a source. "They were very good friends."
Lange has also denied that he is dating Thiébaud, telling PEOPLE
the split was "just a growing apart."
Reporting by SARA HAMMELFor more on Thiébaud, the high-profile split, and how Twain is coping, pick up PEOPLE, on newsstands Friday.Like this story? Click on the Yahoo Buzz! button below
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