[Event "Chess Riddles: Add the king & mate in 1 - Riddle"] [Date "2025.10.25"] [Result "*"] [Variant "Chess960"] [ECO "?"] [Opening "?"] [StudyName "Chess Riddles"] [ChapterName "Add the king & mate in 1 - Riddle"] [ChapterURL "https://adjva4.dpdns.org/study/7QTOaGiW/pBPgFhoN"] [Annotator "https://adjva4.dpdns.org/@/adapodadeiii"] [FEN "8/1P6/kP6/3Q4/K7/8/1R6/R7 w - - 0 1"] [SetUp "1"] [UTCDate "2025.10.25"] [UTCTime "09:55:07"] [Orientation "white"] { Here neither the black king is to place on ‘c1’ along with ‘1.0-0#’ as his route via ‘d1/d2’ would have made castling inadmissible, nor on ‘f3’ along with ‘1.0-0#’ which seems to be successful. But the square ‘h1’ is dark. So the board must be turned by 90◦ (with white's king on a4). Then you add the black king on a6 (the square a6 was ‘c1’ before the rotation) and mate by an underpromotion. You need to rotate the board by 90 degress! - That was the Key. } 1. b8=N#!! *