What can kill Godzilla? Honest question.

Hello everyone! Besides three headed alien dragons along with other monsters, and a fictional weapon(Oxygen Destroyer), what can kill Godzilla? Yeah yeah I know, he's a fictional character, but this makes for good discussion. Plus, I really don't know. Im sure you all can tell me. Now in regards to the new movie, Godzilla will represent(Said by Gareth Edwards) the Force of Nature and or the Hand of God. 
Realistically, nature can never be completely stopped. So is Godzilla arguably unstoppable? I've heard that a nuke can kill him. If so, that is rather..strange. Then again, what created you can destroy you I guess. So if a nuke can kill him, why hasn't it been used? lol I want to believe in my mind that Godzilla is superior to the monsters in Pacific Rim, as well as those in his own universe. The Pacifc Rim kaiju(Although created by aliens) were just giant beasts with tough skin. Godzilla is an atomic creature, fully composed of extreme radiation. If he were to be killed in the new movie, or the older ones with the acception of the first movie and "Godzilla vs Destoroyah", what is something we actually have that is capable of killing him? Would it be a nuke? Educate me! lol