Breeches were worn before this. Brummell lived in the late 18th century and early 19th.

Remember, trews in their original form, are not really trousers like we know them. They were more like breeches and were skin tight. Interestingly enough, the same firm that made Beau Brummell's trousers recently made a pair of REAL trews for a friend of mine, cut on the bias of course. I have yet to see the finished result, but I have been assured that they are beautiful and will make quite a splash at the Oban Ball.