Regex that matches a newline (\n) in C#

OK, this one is driving me nuts.... I have a string that is formed thus:

var newContent = string.Format("({0})\n{1}", stripped_content, reply)

newContent will display like:
(old text)
new text

I need a regular expression that strips away the text between parentheses with the parenthesis included AND the newline character.

The best I can come up with is:

const string  regex = @"^(\(.*\)\s)?(?<capture>.*)";
var match= Regex.Match(original_content, regex);
var stripped_content = match.Groups["capture"].Value;

This works, but I want specifically to match the newline (\n), not any whitespace (\s) Replacing \s with \n \\n or \\\n does NOT work.

Please help me hold on to my sanity!

EDIT: an example:

public string Reply(string old,string neww)
        {
            const string  regex = @"^(\(.*\)\s)?(?<capture>.*)";
            var match= Regex.Match(old, regex);
            var stripped_content = match.Groups["capture"].Value;
            var result= string.Format("({0})\n{1}", stripped_content, neww);
            return result;
        }

Reply("(messageOne)\nmessageTwo","messageThree") returns :
(messageTwo)
messageThree