Arguably, the moment Ahsoka realized Darth Vader is her former master. All credit goes to Disney for the video content from Star Wars Rebels, Siege of Lothal S2Ep1, brought to you by Robskind Productions (sort of, thank you Disney for the great show!)
Check out Rebels in 10 Seconds - Season 3 of Star Wars Rebels!
For those wondering why the image is flipped, it's because of copyright concerns. If you want to see the other version, you should watch the full episode from Disney or look for a copy floating around somewhere.