A Sudoku With Only 4 Given Digits?!

You can try this quite remarkable construction by Aad van de Wetering here:
https://cracking-the-cryptic.web.app/...
Normal sudoku rules apply. In addition, both marked diagonals must also contain the digits 1 to 9. Cells that are a knight's move apart (in chess) cannot contain the same digit. The central 3x3 box must form a magic square.

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Hi! We're Simon Anthony and Mark Goodliffe, two of the UK's most enthusiastic puzzle solvers. We have both represented the UK at the World Sudoku Championships and the World Puzzle Championships. We're also "cryptic crossword" aficionados. Mark is the twelve-time winner of The Times championship and Simon is the former record holder for most consecutive correct solutions to The Listener crossword. We hope we can help your puzzle solving while also introducing you to some of the world's best puzzles.

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Simon and Mark