While flying my R/C plane I noticed a nearly invisible craft flying very high above my model. It appeared to at or above commercial aircraft cruising altitude. I followed it (circled) with my model to keep it in my field of view until the model ran out of gas. After landing my RC model I noticed that a private aircraft had also noticed the object and was climbing toward it to keep it in view.((NUFORC Note: Witness indicates that date of incident is approximate. PD))