Music maestro Elton John, 77, is reportedly singing a sour note after being snubbed by Disney and cut out of the upcoming prequel to The Lion King, RadarOnline.com has learned. Despite delivering classic hits for the 1994 animated film, the Rocket Man was not included in the upcoming prequel, Mufasa: The Lion King. “After gifting the studio with such timeless classics as Can You Feel the Love Tonight and Circle of Life, Elton has been blindsided by this egregious snub,” an insider dished to the National Enquirer. “To have his legacy disregarded in such a manner is a bitter pill to swallow. He …