Pope Leo VIII dies. His pontificate was a confused one because, according to official Catholic Church decisions, he was both Pope and Antipope at different times. Between 963 and 964 he was an Antipope because his election to the papacy by the Roman synod was apparently invalid. He was also only consecrated a priest two days after being elected, which was a problem for many.
Pope John XII was returned to the papacy but died suddenly. A new pope was elected, Pope Benedict V, but he only lasted a month before Emperor Otto I the Great returned to Rome. He was the one who forced the Roman synod to originally depose Pope John XII then elect Pope Leo VIII and he wasn't about to allow Pope Benedict V to remain. Rome was forced to accept Leo VIII and since Benedict accepted the change, Leo became a legitimate pope.