If the Dragon of Mars is the Void Dragon, How Did the Emperor Get to Mars in the Middle Ages?

The story goes that the Emperor defeated a dragon in the Middle Ages, giving rise to the legend of St. George. It’s also implied that that dragon is the Void Dragon, and is imprisoned on Mars (influencing the AdMech).

But does that mean that the Emperor somehow flew to mars during Medieval times to plant the dragon there? Or that he fought the dragon on mars, and people somehow got word of it and made the legend? Or did he keep the dragon on Earth for a few millennia before relocating it to mars?