That's a tough one. I see no reason to really warn him honestly. A lot of times with myself I leave it be unless I am asked. To be honest. i really don't think there is a wrong way to go about it. Its really up to what you feel most comfortable doing. if you feel more comfortable giving him a heads up, then I say do it, cause it will put you at ease. If you are not comfortable telling him before he sees it, I would let it go unless he asks about it.