How to remove "(" from "8,99 € (43%)"?

I have the text "8,99 € (43%)" and I just want the number 43.

I used "[?<=(] ?[\d]+", but the result is "(43". How to remove the "("?

Thank you in advance.

Is the number always followed by "%" ? If so, you can just use:
\d+(?=%)