Gurgustius (Welsh: Gwrwst) was a legendary king of the Britons as accounted by Geoffrey of Monmouth.

He came to power in 788BC.

[1] He was the son of King Rivallo and was succeeded by Sisillius I, and then Jago, who was Gurgustius' nephew.

Geoffrey has nothing to say of him beyond this.

[2] The Book of Baglan (1600–1607) gives Gurgustius' name as Gorwst, and states that his second son, Antonius, was Duke of Cornwall.