I was going through some old mail when I came across this. It's a chess problem I found few years ago and sent to a friend. I've been a huge fan of chess problems since as far as I can remember, and this one is by far the best I ever saw. It took me an hour or so before the solution struck me.

It appears deceptively simple. Made of 2 parts, and the first one is extremely easy. It's the second one that is interesting.

White mates in 2
a) Assume Black can't castle (very easy).
b) Assume Black can castle (not so easy).

Also, did anyone by any chance come across this before and knows who the author is. The guy must have been a genius. However after googling and looking through the internet I can't find it anywhere. Please let me know if you know who the author is.

EDIT: Please, in order to avoid spoilers, don't post the solution to part (b) directly. Instead if you want, use https://pastebin.com/ and post there then give the link here, or post it in an attachment.

EDIT 2: Well, the discussion below has spoilers. So before reading on, see if you can figure this out yourself.

It's nice, but not that hard. KG6, then either RD8 or in case of castle h7.

https://www.chess.com/blog/danheisman/a-very-clever-problem

Spoiler alert, the link contains the solution.

Isn't KG6 folliwed by RH6?

If not castle, then RE6.

Nope. After Kg6 Black responds with Rg8x and white can't mate in 2.

No. KG6 would be followed by black: RG8# ... then white has to get out of check somehow and the 'Mate in two' condition is already not met.

Thank you!!!

Did you come across this before? Or did you just find it now?

Ah, I haven't taken into account rx6. Yes Ke6 then is the correct solution.

I've never seen this before. Tried googling a couple of phrases and it was the second one for "chess problem mate in two black can't castle". ;)

Ke6 is the correct solution for the easy part (a).

Now, what about part b?

(Also, would I call this the best problem ever, if the solution was anything this simple? ;))

Oops yes, it's K not R, I always confuse letters in chess.

Did anyone find the mate if castle is possible?

That makes me sad. My google-fu is abyssmal.

But Ke6 works, if no castling is allowed

Ho ho ho I found it :)

Edit to hide

Ah, but firstly I wasted some time trying reverse image search which was not very effective.