Godzilla sets things right when he battles Ghidorah for the third time in the movie and destroys him while in his burning form. Following his victory, Rodan and the other Titans respond by bowing in respect to Godzilla, which effectively crowns him as the new King of the Monsters.

In their efforts, the organization discovers the Titans, a pack of monsters comprising of Godzilla, Mothra, Rodan, Ghidorah, Kong, Behemoth, Methuselah, Mokele-Mbembe, Scylla, Abaddon, Bunyip, Baphomet, Leviathan, Na Kika, Tiamat, Sekhmet, Yamata No Orochi, Typhon, Quetzalcoatl, Amhuluk, and Camazotz.

In this pic you can see all the monsters bowing to Godzilla.

The members of Monarch, an crypto-zoological organisation, must rely on the Godzilla and Mothra to defeat King Ghidorah and Rodan, after the former awakens other dormant Titans to destroy the world.

She's been called the Queen of the Monsters, and she is perhaps the most beautiful and mystical of the classic Toho kaiju. ... Mothra was the first of the kaiju to receive title billing alongside Godzilla, in 1964's Mothra vs. Godzilla.