Antipope Constantine II

Not the brother of Desiderius, King of the Lombards

https://en.wikipedia.org/wiki/Antipope_Constantine_II

Antipope Constantine II (died c. 769) was a Roman prelate who claimed the papacy from 28 June 767 to 6 August 768. He was overthrown through the intervention of the Lombards and tortured before he was condemned and expelled from the Church during the Lateran Council of 769.

Upon the death of Pope Paul I various factions contended to secure the appointment of their respective candidates as pope. Constantine, although a layman, was supported by a group of Tuscan nobles, led by his brother. They secured his election by force of arms. The following spring, local authorities, with Lombard support, succeeded in deposing him. The Lombards then attempted to install their own candidate, a priest named Philip. He, in turn, was overthrown the same day by the local authorities who then elected the churchman Stephen. For a short time Constantine retained some support outside the city, which resulted in armed conflict. The supporters of Stephen had the imprisoned Constantine blinded, which, it seems to be generally allowed, Stephen was unable to hinder.[1] After that, Constantine was held in close confinement in a monastery. He is today considered an antipope.

https://es.wikipedia.org/wiki/Constantino_II_(antipapa)