An "Ah-Ha" Moment!

I was perusing eBay one day and came across this photo.  It was taken on the set of Possessed (1931), starring Joan Crawford and Clark Gable.  Nifty photo with all the lights, puddles of water on the 'street', the cameraman on a crane setting up a shot.  What caught my eye was the gent in the polo outfit with his back to the camera.  It's our Bob! 

And how do I 'know' it's him, you may ask, since the vendor did not have anymore data on the still but the name of the movie. Well .... 1) Possessed began filming Sept. 21st.  Bob has returned to Los Angeles after his summer break, filming of Private Lives would begin soon.  So, Bob is both in town and not busy with filming his own movie.  2) He was quite interested in cameras and all aspects of filming movies, so his observing a scene being setup on an MGM set would not be out of the ordinary.  3) Both Bob and Clark played polo during this period of time.  The two leaving the studio for or returning from a game together would be a possibility.  And 4), that's Bob's polo outfit!  The long camel-haired jacket with the large upturned collar and riding boots was de rigueur for polo enthusiasts, an outfit worn often by Bob ... he looked so darn good in it.  

And what caught my eye initially ... those long skinny legs, narrow shoulders, the hairline and side burn ... quite simply it is Bob!!  At least I'm 98% sure it is!  What do you think?  Anyone know for sure?  Do let us know.  Meanwhile, I'll just enjoy the rather nifty photo.