Actually Alex isn't really the guy to hold Grudge's he does hate Grayson and Xaviere, but Grayson saw him like Jean Paul and didn't want him to be Robin due to his brutality, it would be crazy for him bring up how he was Robin and tell Xaviere about it, it would bring up a funny how do you know that moment. 

I'mma have him attack now since he already over heard most of what everyone said about each other and knows Xaviere is Robin now.