Silver and diamond in same ranked game

So today I played a game where the enemy mid-laner was silver 1 and our support was diamond 5. How is this even possible? I understand playing against golds but in my opinion a silver player should not have to play against a diamond player in ranked. I think that its not fair that he/she had to play against a diamond rank player to climb in silver. Is this a bug or is it normal that silvers and diamonds play in the same game?
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