How to friend zone someone as nicely as possible?

[Banana]

My best male friend of almost 3 years messaged me on Facebook today. He asked me if there was a chance that we could be something more than friends.
I'm not interested in him that way. It really breaks my heart that I'm going to have to reject him. I still want to maintain our close friendship; I don't want anything to change.
How do I go about telling him this?
If you've ever friend zoned someone, or been put in the friend zone, did your friendship hold up?

[grenize]

there's a lot of my friends who I have had to gently let them know I'm only interested in being friends with them. Believe me, you're doing yourself and the other person a huge favor by clearing the air on that issue. Do not send a public message such as posting on facebook--just call him or talk to him face-to-face, if possible, and let him know that you saw his posting and that you are only interested in being friends with him. Do not elaborate on it unless he asks you to do so. Just keep it simple and move on to another topic so he doesn't feel awkward about it.