He will shed humanity like an old skin.
It's long dulled, dried-out, constricting movement and vision. Yet it still clings to him, its itch a reminder of things that made him up once upon a time--twinkling eyes, the melody of laughter, fading, then endless empty spaces.
But he's turned himself inside out; beneath, his true self has grown brighter, stronger, larger than life.
Oh, there were steps before and after--take invulnerability, quite a jolly old time--but immortality had made him first stretch and strain what he will cheerfully leave behind now.
To be what he has become.