Is that a checkmate?

I was playing this game and somehow after move 21...Nd3, it said that it was a checkmate and black won
Here's the game
1.e4 e5 2.Nf3 d5 3.exd5 Qxd5 4.d4 Nc6 5.Nc3 Qa5 6.Bd2 Nf6 7.dxe5 Nxe5 8.Qe2 Bd6 9.Bf4 Ng4 10.O-O-O O-O 11.h3 Nxf3 12.Qxf3 Nf6 13.Bc4 Be6 14.b3 Nh5 15.Nd5 c6 16.Ne7+ Bxe7 17.Bd2 Qxa2 18.Bc3 Bg5+ 19.Rd2 Rfd8 20.Rd1 Nf4 21.Rd6 Nd3

It‘s even double-checkmate.



It‘s up to you to explain your resentments.

When the knight moved to d3, it also revealed a check from the bishop behind it. Because the king is attacked by both pieces, capturing the knight will not stop check; therefore, the king must move to escape. However, the king has no squares to flee to, so the position is a checkmate.

that checkmate was badass

Morphy would be proud! :]

21. ... Ne2 would have been checkmate as well.

Thanks a lot. I was tired when i played the game and i didn't notice the double checkmate. Indeed, it's a cool checkmate.