VATICAN CITY (AP) — Retired pontiff Benedict XVI will help Pope Francis celebrate the sainthood ceremony Sunday for John Paul II and John XXIII, setting the stage for an unprecedented occurrence of two living popes canonizing two of their predecessors. About 1 million pilgrims are expected at the event and many were flooding into Rome on Saturday.

Vatican spokesman the Rev. Federico Lombardi told reporters on Saturday that Benedict will be in St. Peter’s Square for the canonization of John and John Paul. He said Benedict and many cardinals will “concelebrate” the Mass with Francis.