What are the odds?

I've had that happen before; at least it was a quilava and not a legendary

Happened to me this morning. I had just finished the second round and there was only 2 mons left for the third round when I got locked out by a raid taking over the gym.
I just left. Didn't even bother waiting to see what took it over.

That is most unfortunate. I got zapped by Alakzam too when it was down to the last mon. But I also had the good luck of putting a mon right before a boss took over.

This has happened to me so many times recently, even at around 5-6 a.m. Why the h&ll does Niantic think it's a good idea to remove the egg icon and 1 hour of notice before the raid boss egg hatches? Even a Magikarp boss now has a 2-hour time frame to defeat! Leave this to Legendaries and 4* bosses only. Normal raid bosses don't need that long time waiting in rage. -_-

I was hoping you were going to say you beat the Magmar defender, then a Magmar raid popped up.

I have had similar happen to me, though. I reached a gym controlled by my team, opened it up, clicked to add a defender, scrolled around a few seconds to choose one, then got flipped off by a Lugia that was suddenly raiding it. Only ever managed to get 12 coins that day too.