Complex sentence: Humperdinck later stated in an interview that his manager declining the collaboration offer was, "the most grievous sin ever committed," and that he would have gladly collaborated with the Gorillaz if he had known they asked.
Split into simpler sentences: Humperdinck later stated in an interview that his manager declining the collaboration offer was: "the most grievous sin ever committed". And that he would have gladly collaborated with the Gorillaz if he had known they asked.