When was the last "year of three popes"?

The Year of Three Popes is a common reference to a year when the College of Cardinals of the Catholic Church are required to elect two new popes within the same calendar year. Such a year generally occurs when a newly elected pope dies or resigns very early into his papacy. This results in the Catholic Church being led by three different popes during the same calendar year. In 1978 Paul VI died. John Paul I was elected to as the next Pope, but his papacy lasted just 33 days (26 August 1978 to 28 September 1978). He was then succeeded by John Paul II.