Wikipedia
Ioannes, ( Latin: Iohannes Augustus) known in English as Joannes or even John, was a Roman usurper (423–425) against Valentinian III.
On the death of the Emperor Honorius (15 August 423), Theodosius II, the remaining ruler of the House of Theodosius hesitated in announcing his uncle's death. In the interregnum, Honorius's patrician at the time of his death, Castinus, elevated Joannes as emperor.
Usage examples of "joannes".
Belgian branch of the Netherlandish school was Joannes Okeghem, who was a singer boy in the choir of the Antwerp cathedral in 1443, and is supposed to have been a pupil of Binchois.
The petition of Joannes, who is son-in-law to Thomas, informs us that he is willing to pay the 10,000 solidi due, if we will make over to him the said farms, and all the property of his father-in-law.