Text #1553Cometography: A Catalog of Comets. Series: Cometography. Vol. 1 .
The French text Historiae Ecclesiasticae Francorum Libri Decem (592) notes, “And once, on the kalends of October [October 1], the sun appeared so darkened, that not a quarter part kept its light, but it was murky and discolored, as sackcloth. Moreover, a star, by some styled comet, which had a projection like a sword, appeared over that region throughout a whole year, and the heavens seemed to burn.” George F. Chambers (1889) suggested the comet remained visible for a month, rather than a year.
There was a total solar eclipse on October 3 of this year. It should be noted that Gregory was describing some of the prodigies that preceded the great plague of Auvergne, France. This has been dated as occurring in 571. Since the comet was not directly dated and since it did not necessarily occur at the time of the eclipse, it is probably more correct to assume it was seen sometime between 563 and 571. Therefore, this could be a supporting observation of the comets of 565 or 568, although the latter would seem more likely.
Sources: Historiae Ecclesiasticae Francorum Libri Decem (Book IV). (592), p. 141; G. F. Chambers (1889), p. 565.