Betelgeuse V

Betelgeuse was a planet mentioned by the Fourth Doctor.

When Davros revived and demanded to know what had happened while he was in suspended animation, the Doctor told him that Arcturus had won the Galactic Olympic Games with Betelgeuse coming in second. (TV: Destiny of the Daleks)

Professor Chronotis owned a travel guide to it, entitled Alternative Betelgeuse. (PROSE: Shada)

Jackie Tyler once referred to Betelgeuse as a planet the Ninth Doctor might travel to. (AUDIO: Retail Therapy)

Ian Chesterton also mentioned a star named Betelgeuse. (PROSE: Byzantium!)

Behind the scenes
was a planet in script editor Douglas Adams' The Hitchhiker's Guide to the Galaxy series. In the real world, the star Betelgeuse is not known to have any inhabitable planets in its orbits, but the name "Betelgeuse V" implies that the inhabited "planet Betelgeuse" is the fifth planet revolving around the star Betelgeuse.