Embarrassed: seen being intimate by creep

First of all I know that it was wrong. 
Hubby and I were getting intimate in the car parked outside in an urban area. Literally naked and going at it. 
All of a sudden I saw a pair of eyes looking over at us over the fence and quickly put his head down after seeing that I saw! Mind you it was dark and the windows were glossing over in the front but I'm sure that the creep could see.. 
I haven't brought it up to anyone and felt extremely violated by this..
We just told each other to try to forget it happened