"Braig makes his debut in
Kingdom Hearts Birth by Sleep, taking place a decade prior to
Kingdom Hearts. In the game, he battles
Terra after he seemingly captured
Master Xehanort. The fight ends when Terra, consumed by his darkness, disfigures Braig's face while freeing Master Xehanort.
Later, it turns out that Braig was working with Master Xehanort, and by the time of his next appearance has accepted his darkness (indicated by his remaining eye becoming yellow). He then battles Aqua in the
Keyblade Graveyard. After returning to his world, Braig is the first to find the conscious Terra, now
Xehanort, and is satisfied that his plan has worked. He is however dismayed to find that Xehanort does not recognize him, and his attempts to bring back his memories prove only to annoy him."
Braig - Kingdom Hearts Wiki - A world of information not accessible by Gummiship
So. Braig was technically MX's other apprentice, and the only one who truly retained his memories from BBS other than Aqua and Ansem (If he counts). But he's the only one who knew about MX's master plan, so much that even Xemnas didn't know what Xigbar knew.