He can never tell them the truth. He can never tell anyone the real story. Because he knows that they all hate that man with drums. The man who took over the earth, enslaved their people and ruined their home. They all hate him. They are all so happy that he is dead.
He can never tell them the truth. He can never truly mourn. He can never grieve for that man in the proper way. The way he would if they were still on Gallifrey. Back when the two sunrises set the silver tress aflame. Back before everything went wrong. Now his customs, his traditions have all been lost to him.
He can never tell the truth. Because they'll all hate him too. They won't trust him, not like they do now.
He can never say how much he truly loved him.