Use that to give yourself the gumption to fire him on the spot next time you see him. Don't be rude, of course, but it's all the more reason to be honest and up

Use that to give yourself the gumption to fire him on the spot next time you see him. Don't be rude, of course, but it's all the more reason to be honest and up front and say, "Look - you haven't been able to deliver what we expected when we hired you. We were looking for ... but we've noticed that you're more... You might fit better at a larger corporation, but right now, we really need to let you go."