Foul play has been ruled out. My guess would be his years of substance abuse issues (in and out of rehab) have caught up with him and even though he was probably clean his body just packed in. To the naked eye he had a great life. In a popular show, adored by millions around the world, could sing, good bank balance and about to marry the hot lady the show is built around. But something must have been bothering him to go onto drugs in the first place. He went from being an unknown nobody to being the lead guy in a hugely popular show with overnight success. I can imagine that would have been alot to take in.