So of all the things we learned in "The Core and The King", probably the second most interesting to me is that it changes the context of Andrias previous(Rather inaccurate) flashback.
The scenes with Andrias, fully grown, the throne and the city pulsating with the power of the combined gems power rather than just heart, and his friends by his side as he sits the throne never happened.
But that doesn't make this unimportant. It just changes the context from "What happened", to "What Andrias WISHES had happened".
Even now, a thousand years later, this is what Andrias dreams of, his greatest desire. Not conquest, but to just rule Amphibia with his friends at his side. The way it was meant to be. The way it SHOULD have been.
It is also a world that cannot be. No matter what he does, he cannot bring these two back to him.
It is very much in keeping with his character. Andrias is a man stuck in the past, which is why he's so stuck on recreating the Amphibian Empire that was his birthright.
It is much, much easier to do that, than to face the fact that he lost Barrel, not due to betrayal, but his own shitty actions, which ultimately lead to his death.
Andrias does not have the stones to admit that whatever happened with Leaf, he and he alone, was the one who fucked up in his relationship with Barrel and got him killed.
Andrias refuses to take personal responsibility for his own actions and mistakes as a person, Instead, he shirks the blame, and throws himself into "Redeeming" himself by recreating the Amphibian Empire that he blames himself for the destruction of.
In that regard, he is the complete and total opposite of Anne, who after having made the worst decision of her life, refused to deny her share of the responsibility.
Andrias needed to learn to accept his own faults in how the trio disintegrated, and then move on from there. Instead, he is still stuck where he was a thousand years ago when Leaf's betrayal was still fresh and raw.
Inside, he is still that teenager who in anger sent his remaining best friend to an assignment that lead to his death, and even now, all these years later he refuses to take responsibility for it.
Andrias needed to let go of the past, and embrace the future that was open to him. But he never did.