Brewer's: George, Mark, John
(SS.). Nostradamus wrote in 1566:
Quand Georges Dieu crucifera, Que Marc le ressucitera, Et que St. Jean le portera, La fin du monde arrivera.
In 1886 St. George's day fell on Good Friday, St. Mark's day on Easter Sunday, and St. John's day on Corpus Christi—but “the end of the world” did not then arrive.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894