After this touching video about a double rainbow went viral earlier this month, I remembered I'd taken a shot of a double last August that had been pretty neat, and from what the guy said in the video wondered if mine had possibly been a triple.
First, the original shot:
I tweaked the exposure shadow level on the original pic, and sure enough, once I darkened it I could see a very faint, third rainbow beneath the lower/brightest arc:
Very cool discovery -- I had no idea I'd photographed three instead of two. Thank you, rainbow guy. :)