Jack shrugged, moving to another chair, leaning forward, his elbows on his knees as he picked up a random book, just to have something in his hands.
"Time War," he said succinctly, watching Susan. "Don't know how it happened in your universe, or even if it happened, but it was hell on mine. Changed history, destroyed worlds. Ended when the Daleks tried to attack Gallifrey. Took their entire fleet, left the rest of the universe to itself while they went to take out the Time Lords. Instead, the Doctor destroyed them. And Gallifrey. And almost himself."
He grinned a little, looking down a second before meeting Susan's gaze again with a hint of mischief in his expression. "Had a daft set of ears when I ran into him again after. And his companion..." He shook his head, chuckling. "I don't know where or why he picked up Vain, but she kept him on his toes. He needed that after the War."
He didn't mention that most people didn't know how history had changed, since he didn't know how he remembered the old history. One spattered with Daleks, and species that had vanished in the changes. Been wiped out by the ripples of change from the destruction of Gallifrey and the Daleks. Most of them. Their final destruction had another effect that he really didn't want to talk about, either.