The cup was not visible from the tee box on the 6th hole at Fox Run. I hit a six iron that landed on the green and disappeared as it tracked towards the cup. The next player hit a similar shot that looked like it was closer than mine. As we approached the green, we saw that a ball was in the cup. We all thought it was the other players ball, and we began celebrating with him. I went to mark what I believed was my ball on the green and realized it was a cally. I yelled, "dont touch that ball!!" As i got to the cup, i saw the Pro V 1 with my standard two blue dot marking. My excitement was a bit tempered by my partners disappointment that he just lost what he believed was his first Hole In one.