We do not know. From Mark 15:40–41 we learn that there were other people who followed Jesus in addition to his disciples. Perhaps they were a large crowd and they followed him into the area of Caesarea Philippi. Presumably Jesus and his disciples would have quiet moments by themselves where he spoke only to them. Now however, Jesus wants to convey a message not just to his disciples but to all those who would seek to follow him.
34 And calling the crowd to him with his disciples, he said to them, “If anyone would come after me, let him deny himself and take up his cross and follow me.