Tennant
The doors to the TARDIS opened, the Doctor passing through into the Executor's ship. Max and Stewart were set up in their new home in London at the dawn of the Industrial Revolution. Stewart could live out the rest of his life seeing his ideas growing to non-universe-destroying theoretical conclusions.
"Sorry to keep you on the bench, but I've learned quite a bit over the years," the Doctor said, leaning against one of the chairs.
From his command seat, the Executor smiled. "I don't know about that."
"Oh?" the Doctor asked.
"History has proven that you are capable of unimaginable atrocity when the universe is at stake," the Executor said. "Were it not for me playing the role of heartless assassin, it would have been you. When pressed, you would not have hesitated. I enabled you to step back and see your solution. Just what you needed."
"That is a theory," the Doctor said. "How do you support it?"
"The absence of Gallifrey," the Executor said simply. Behind him a star chart displayed a system in the Kasterborous Constellation with its missing planet. "You did it then?"
The Doctor nodded grimly.
"The only solution for a terminal condition," the Executor said. "If only you'd been able to step back."
"Something I've thought about every day since," the Doctor lamented. He sniffed and stood straight. "So what now, back to your padded room?"
The Executor shook his head. "I've never seen the universe without the Time Lords." He tossed the Doctor his fob watch. "Keep it handy though."
"I hope not to have to use it," the Doctor said, tucking it into a pocket. "I'm here if you need me."
"I know," the Executor said.
The Doctor bowed at the waist. "Lord Executor."
The Executor nodded. "Lord Doctor."
The Doctor threw the Executor a salute before turning and heading through the door as it irised shut. The Executor turned back to his console, several screens appearing with star charts and other information. On the screen to his right was live image of Max and Stewart outside their new home. The Executor stared at the boy. The boy seemed to stare back at him. Tapping a button, he turned off the screen. He tapped two more buttons, kicked the peg at his foot, twisted the throttle and took off.
The Executor
Back inside his TARDIS, the Executor's TARDIS disappearing behind him, the Doctor approached the controls. He flipped several switches and pulled the main control lever. River took a place at another panel and assisted.
"So, two Time Lords now?" she said.
"For now," the Doctor agreed.
"How do you feel not being the last anymore?" River asked.
"Worried," the Doctor said. "For a long time, the same look little Stewart had could be found in the Executor's eyes. When I think about what it took to extinguish it…"
"Do you believe he'll go back to the way he was?" River asked.
"I don't know," the Doctor said. He reached into his pocket and pulled out the watch. After a moment, he tucked it back into his pocket. Turning to River he grinned. "So?"
"So indeed," River countered.
"Dinner at your parents to make up for leaving them behind?" asked the Doctor.
"Sounds delightful," River said pressing several buttons. "Fancy a swim on the way?"
"Sounds disgraceful," the Doctor said with a grin.