The Master walked headed towards teh Doctor the moment he saw him, well felt him. He looked, well obviously different from the Doctor he remembered in school, but familiar too. He blinked and paused. This was the man in his dreams, the one begging him to regenerate. How odd. His adult memories were locked away but bits and fragments still floated about making no sense.
This Master was actually the regeneration after Saxon was shot. However, when he regenerated, his brosken laser screwdriver had come into play. Mort importantly the lazarus technology embedded into the screwdriver, hence the child body and no real memories past the time he was ten. He had no clue he was any older or different than the child who he was when he attended the Academy with his friend the Doctor.
So, he smiled a genuinely friendly smile for the Doctor as he approached. "Doctor! It's good to see you, even if you are a bit older than I remember." He rocked back on his heels and grinned. "No rip roaring adventures for me yet, but I'd wager you two have had plenty." He nodded back to Saxon. "And apparently this place is safe as Gallifrey itself. A place for people to recover." He frowned, then asked. "I don't suppose you remember why I regenerated just now do you? I can't seem to recall." And that was bothering him more than just a little.