How Did I Get my Killer King Achievement?

Just recently, when I scrolled through my achievements page, I found out that I have Killer Queen, Killer Pawn, Killer Bishop, Killer Knight, and Killer Rook. 

“Is there a Killer King achievement?” I asked myself.

I tried to search in Internet, and I found out that there is!

Well, I think for a second to know how can I get that achievement. Then, suddenly I gave up because I didn't know how. I figure it out on Internet that I need to discovered check in order to got that achievement.

I tried it by myself to know if it is true. I manage to setup the gameplay. The gameplay is quite surprising, because you may found lots of blunders.

If you wonder how did I did this. I played the whole board all by myself. Yes, this one shouldn't be practiced because—you know it is illegal.

After that, I see this achievement on my account.

Some say it is elusive to get...and here's my story how did I get that!