The high priest said to him, “I charge you under oath by the living God: Tell us if you are the Messiah, the Son of God.” “You have said so,” Jesus replied. “But I say to all of you: From now on you will see the Son of Man sitting at the right hand of the Mighty One and coming on the clouds of heaven.” Then the high priest tore his clothes and said, “He has spoken blasphemy! Why do we need any more witnesses? Look, now you have heard the blasphemy. (Matt 26:63-65)
This verse is related to Ps 110:1 when King David writes about “his Lord”.
The Lord says to my Lord: “Sit at my right hand until I make your enemies a footstool for your feet.”
The Jews understood that the Messiah talked about in the Old Testament was God. In the above verse, King David says that his Lord (referring to the Father” calls his Lord (referring to the Messiah) “Lord” and asked Him to sit at His right hand.
When Jesus claimed to the the one referred to in this verse, the high priest immediately understood his claim to deity and tore his clothes because he believed Jesus was speaking blasphemy.