Throneworld
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A Throneworld was an important planet in an empire, presumably serving as a capital.
Pluvikerr was the Throneworld of the Gubbage Cone Empire. (PROSE: The Crystal Bucephalus) The Master later stole a Vortex Cloak from the ruins of the Gubbage Cone Throneworld. (PROSE: The Quantum Archangel)
Phaester Osiris was the Throneworld of the Osirian Court. (AUDIO: The Ship of a Billion Years, PROSE: The Sands of Time)
In an alternate timeline where Rassilon and the Cybermen invaded all of time and space, all the throne planets of the Sontaran Empire were destroyed. (COMIC: Supremacy of the Cybermen)