Funny mate

White to move, mate in 1
lichess.org/editor/8/8/8/3B4/8/8/r5pp/R1K4k_w_-_-_0_1

I must ask - is it a position in Chess960 variant?

This is a standard position. No variants.

I just figured out that this is impossible if king is on c1, but possible if king is on e1. The move is:
1. O-O-O#
EDIT: The original position is a mate in 8.

The position is right, the king is on C1. And it is really a mate in one. No mistakes here.

Reanalysed the position with my engine three times, no mate in one ^^

This can only be an April fool's joke.
According to the diagram in #1 white has no castling rights left. Even if this were a 960chess position, white could not castle long.
Therefore white can never give a checkmate with the rook in this position.
The only legal check for white in this position is Bxg2, but this is of course no checkmate.
It will be interesting to see what kind of solution @Zvneskaia will present for this puzzle.
Maybe he will edit the diagram and add long castling rights ? He has still 2 hours left to edit his posting.

I remember that I once tried to solve a similar puzzle with the same idea. But I didn't know that it was a 960chess position in which long castling was possible. That was the day when I learned how to castle in 960chess. You have to move the king onto the rook. In this case Ka1 would be the solution.

Edit: Check out this study. lichess.org/study/Jwm0DzSq
The story in this study is just as funny as this puzzle here.

The link was a Board Editor link, not an Analysis Board link.... @Zvneskaia Does that mean anything?

If its standard chess not even chess960 or "chess in a board editor - variant" like the tasks "transfer one match to make the mathematical equation valid" :) - there you could transfer the rook from A1 to D1 no matter where the white king is.

- there is no stalemate
- there is no mate-in-1 for black

@Zvneskaia - are there 3 mate in 1's with 3 different "moves" ?
Can the mate in 1 also work out here - lichess.org/study/ZVicBGWB?