Let us first recall the reference to the "Bishop in white" made in the "third part of the secret", made public on May 13, 2000:
“J.M.J.The third part of the secret revealed at the Cova da Iria-Fatima, on 13 July 1917.I write in obedience to you, my God, who command me to do so through his Excellency the Bishop of Leiria and through your Most Holy Mother and mine.
After the two parts which I have already explained, at the left of Our Lady and a little above, we saw an Angel with a flaming sword in his left hand; flashing, it gave out flames that looked as though they would set the world on fire; but they died out in contact with the splendour that Our Lady radiated towards him from her right hand: pointing to the earth with his right hand, the Angel cried out in a loud voice: ‘Penance, Penance, Penance!'. And we saw in an immense light that is God: ‘something similar to how people appear in a mirror when they pass in front of it' a Bishop dressed in White ‘we had the impression that it was the Holy Father'. Other Bishops, Priests, men and women Religious going up a steep mountain, at the top of which there was a big Cross of rough-hewn trunks as of a cork-tree with the bark; before reaching there the Holy Father passed through a big city half in ruins and half trembling with halting step, afflicted with pain and sorrow, he prayed for the souls of the corpses he met on his way; having reached the top of the mountain, on his knees at the foot of the big Cross he was killed by a group of soldiers who fired bullets and arrows at him, and in the same way there died one after another the other Bishops, Priests, men and women Religious, and various lay people of different ranks and positions. Beneath the two arms of the Cross there were two Angels each with a crystal aspersorium in his hand, in which they gathered up the blood of the Martyrs and with it sprinkled the souls that were making their way to God.Tuy-3-1-1944”. [Source]
The Vatican explanation at the time was that the "bishop dressed in white" was then reigning Pope John Paul II, whose life had almost ended on another May 13 (1981), with a murder attempt on St. Peter's square: "As regards the passage about the Bishop dressed in white, that is, the Holy Father—as the children immediately realized during the 'vision'—who is struck dead and falls to the ground, Sister Lucia was in full agreement with the Pope's claim that 'it was a mother's hand that guided the bullet's path and in his throes the Pope halted at the threshold of death' (Pope John Paul II, Meditation from the Policlinico Gemelli to the Italian Bishops, 13 May 1994)." [Same source as above]
Now, in the official missal of his visit to Fatima today and tomorrow, in the Prayer specially written for this day, Francis identifies himself as the "bishop dressed in white":
Hail Holy Queen, blessed Virgin of Fatima, Lady of the Immaculate Heart, refuge and path that guides to God! Pilgrim of the Light that we receive from your hands, I thank God the Father that, at all times and places, acts in human history; pilgrim of the Peace that you announce here, I praise Christ, our peace, and for the world I ask for concord among all peoples; pilgrim of the Hope which the Spirit encourages, I want to be prophet and messenger so as to wash the feet of all at the same table that unites us.Hail Mother of Mercy, Lady of the white robe! At this place where one hundred years ago you showed all the designs of our God's mercy, I look upon your robe of light and, as bishop dressed in white [como bispo vestido de branco], I remember all those who, robed in baptismal white, want to live in God and pray the mysteries of Christ to attain peace.
OK, then.
