c# regex to remove string part, C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var input = @"{""t"":1,""i"":""a32dffdd-c99d-4df5-9296-9ae5fb024dc1"",""p"":""At DB Server Time: Wed Sep 27 2017 05:27:18 GMT+0000 (UTC), you sent this message: {'t':1,'i':'a32dffdd-c99d-4df5-9296-9ae5fb024dc1','p':{'u':'/test/delayed','v':'GET','h':{'X-BH-AgentID':'testagent','X-BH-TempToken':'testagenttemptoken'},'p':'','t':{'t':1000}}}""}";
            var pattern = @"At\s+DB\s+Server\s+Time:\s+\w{3}\s+\w{3}\s+\d+\s+\d{4}\s+[0-9:]{8}\s+GMT\+\d+\s+\(UTC\)\s*,\s+you\s+sent\s+this\s+message:";
            var result = Regex.Replace(input, pattern, string.Empty);
            
            Console.WriteLine(result);
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,14 sec, absolute running time: 0,17 sec, cpu time: 0,19 sec, average memory usage: 17 Mb, average nr of threads: 4