Shania Twain's longtime assistant denies affair reports

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.

"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."

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