c# Path.Combine isn't working right?

I'm trying to combine a path and a string to create a path, although the path is the string only? what I mean is, when I use Console.WriteLine(filepath) all that comes out is the string and not the path, and when I write the argument (whats used as the path, its a argument you set when you open the .exe) its comes out properly, as the set path, as the string:

string filepath = Path.Combine(arg1, @"\tf1.dat");

arg1 is the argument turned into a string.