The letter that patriarch Kyros of Alexandria sent in 638 to his colleague Sergios of Constantinople, and in which he enthusiastically endorsed the “Ekthesis” of Heraclius, contains a chronological contradiction. I will try to show that the problem can only be removed by amending the chronology of the bishops of Rome proposed by Louis Duchesne in 1886. I will argue that Duchesne made two mistakes that affect all the dates of the popes between 619 and 649. The consequences are manifold; I will focus only on those that pertain to the disgrace and trial of Kyros - a key event for the understanding of the last years of Byzantine Egypt. I will reassess the famous papyrus P.Lond. I 113.10 and will try to show that, far from proving Kyros’ presence in Alexandria in 639/40, it in fact supports the traditions on the “Kyros tribute” paid to the Arabs in the years before the final conquest in 641.