I was on a short IFR trip and under ATC control. Level at 10 grand while on AP. I had a Challenger cross in front of me from left to right and it had to be less than 50 feet from hitting me. I had a real nice view of it and could have told you the color of the pilots eyes! It was only then ATC started asking us both if we saw each other. I have NEVER had a midair during the cruise portion of a flight.
Just curious if anyone has ever had a midair.

Conditions- Mytraffic,Ultimate traffic others are fine. In and around large airports especially during the approach/final phase does not count.