Barrowman's husband Scott Gill unknowingly walked into the frame with his penis fully exposed while the actor was chatting.
Barrowman had been discussing the Palm Springs weather when Gill and his appendage appeared in front of the thousands watching at the time.
"Everybody just saw you naked," Barrowman tells his spouse. "Did you all see him naked?"
Um, yah, we sure did.
You can cut to the full-frontal surprise by moving your cursor to the 1:55 mark below (or -5:12 if you're measuring from the timestamp on the right side of the video).
H/T The Gay UK