Menashe Kills Yeshaya HaNavi
The wicked King Menashe, Chizkiya's son, brands his grandfather Yeshaya HaNavi a false prophet over the fifteen added years, and puts him to death.
Unfortunately, the plan did not succeed. Chizkiya’s son was the wicked King Menashe. The Gemara (Yevamos 49b) states that Menashe determined that Yeshaya was a false prophet.
Moshe Rabbeinu indicated in the Torah that the best blessing a person can achieve in regards to his lifespan is to live the full number of his predetermined years. Yet, Yeshaya HaNavi prophesied that Hashem added 15 years to Chizkiya’s life, more than his predetermined years. The contradiction is actually a good question. There is a debate in the Gemara about what the correct answer is. Yet Menashe did not want to hear the answer – he was just looking for an excuse to kill Yeshaya, and so he declared Yeshaya HaNavi to be a false prophet. The penalty for such an offense is death.
Yeshaya HaNavi died at the hands of his own grandson, the wicked King Menashe.