When he wanted to leave, it happened that Merlin came that way in the likeness of a strong peasant and began to write, on the end of the stone, letters of gold that said, IN THIS PLACE WILL MEET IN BATTLE THE TWO MOST FAITHFUL LOVERS OF THEIR TIME. AND THIS BATTLE WILL BE THE MOST MARVELOUS OF ALL TIME, AND NEITHER WILL DIE.

When he had done this and had looked at the inscription, he began to write in the middle of the stone two names: one of the names was LANCELOT OF THE LAKE and the other TRISTAN.

Post-Vulgate Merlin