Shania Twain will serve as a key advisor on Season 12 of NBC’s The Voice, appearing as a mentor to the show’s remaining contestants on April 24. Twain revealed the news on Twitter Thursday (4/13), saying, “Excited to announce that I’ll appear on @nbcthevoice this month, as a mentor to the finalists.”  Shania is no stranger to mentoring singing competition contestants, as she once served as a guest judge FOX’s American Idol.