He knows Lu Ten is dead. He will never pretend otherwise. His son came into this world the day his wife left it, and since that beautiful and terrible day, he has always strived to be there for him, to take advantage of every moment they had together. That is not to say that he was never busy or distracted; he was the crown prince, and the nursemaids and nannies and tutors were a blessing. But Iroh's memories of his own father were cold and sterile; being dressed up and presented to the man on the throne of fire. He tried with all his might to make sure that his son really knew him, and he really knew his son. They fought, they bickered, they argued, but in the ways of a father and a son, not a king and a subject. Lu Ten was his child, his friend, and his world.
Of course, the problem with really knowing someone is that you cannot replace them when they are gone. It would have been so easy, too. He returned from Ba Sing Se, and Zuko was right there. Rejected by Ozai, abandoned by Ursa, made vulnerable by Azula. It could have been a second chance, a way to never lose Lu Ten. He could have his son back.
But that would have been a disgrace to Lu Ten and Zuko both. They were two different people, two different boys in many ways. Lu Ten had been jovial where Zuko bristled. Lu Ten had been calm where Zuko was livid. Lu Ten had been warm where Zuko was hot. And Lu Ten had been Iroh's, where Zuko was Ozai's. Pretending otherwise would be a dishonor to everyone involved.
So he loved Zuko on a new set of terms. He mourned his son by raising his nephew. He guided him, strived to know him too, comforted him as Ozai moved farther and farther away. He could have the crown, for all Iroh cared. Ozai could not see what he was missing. Hopefully it would not take losing Zuko for his brother to realize the blessing he had. No matter his feelings for his brother, he would not wish that pain on anyone.
