The string should be 6 - 20 characters in length. And it should contain 1 Capital letter.

I can do this in code using C#

      string  st = "SomeString"

      Regex rg = new Regex("[A-Z]");
      MatchCollection mc = rg.Matches(st);

      Console.WriteLine("Total Capital Letters: " + mc.Count);

      if (mc.Count > 1)
      {
        return false;
      }

But what i really want is a Regular expression that will match my string if it only contains one capital. The string can start with a common letter and should have only letters.

Thanks In advance. (I did look at some of the other RegEx questions but they did not help).