Thinking about the "Son of God"
Is that what Peter had in mind? Almost certainly not. At the time, "Son of God" was a kingly title, much the same as "Messiah" (which is the first half of Peter's confession). The King is called the Son of God: he is the man on earth who rules by God's appointment. God says of David "You are My Son, today I have begotten thee." And of David's seed, God promises "he will be a Son to me." So "Son of God" means "king."
The thing about human kings, however, is that they keep dying. There can be no ultimate Son of God whose kingdom shall have no end until there is a man who does not die. That might have been Adam, who was God's Son; he would have lived and ruled for centuries over all his descendants, guarding the way to the tree of the knowledge of good and evil until the day God finally gave it to him to eat, that he might die, and lead the way through death to resurrection for all his race.
Well, that didn't happen.
So God the Son became the Son of Man (son of Adam) and the Son of David that he might rule as the Son of God, and after dying be raised to rule forever as both David's Son and David's Lord.
When the High Priest questions Jesus he asks "are you the Christ, the Son of God?" -- the same kingly language as Peter's confession. Had Jesus admitted to that charge only, he would have been in enough political trouble to push the case to Pilate for treason, but Jesus added, "But I tell you, from now on you will see the Son of Man seated at the right hand of Power and coming on the clouds of heaven." That moved the case from kingship to divinity, and the High Priest was able to jump to a blasphemy charge that he hadn't been looking for. The council also could dismiss all the false witnesses they had recruited, because the council were all witnesses who had heard Jesus' words.
At that point the High Priest tore his robes. I know it was customary for folks to tear their clothing as a sign of crushing grief. But this is the High Priest. His robes were the covering of glory and beauty, sprinkled with blood at his investiture, that allowed him to enter the holy place on the day of atonement. Seems like this High Priest, in calling for the death of Jesus, is tearing his robe of office and ending his right to function. The new High Priest is standing there before him, his robe soon to be blood-spattered that he might enter the heavenly sanctuary, once for all.