Bring an application window to the front if I try to open another instance

Question

I have the following requirements to fulfill in a WPF application:

• When you open the program (by clicking its shortcut or double-clicking its executable), it opens its MainWindow normally;
• If you try to open it while another instance is running, instead of opening another window, it brings the already-running to the front, and closes.

Currently I have already a way of detecting an open instance, by using Mutex, but I don't know what I could do to call that instance's MainWindow to the front.

public partial class App : Application
{
    public static Mutex mutex;

    [STAThread]
    public static void Main(string[] args)
    {
        if (!IsFirstInstance())
        {
            CallOtherToFront();  // how to implement this??
            return;
        }

        var app = new App();
        app.InitializeComponent();
        app.Run();
    }

    public static bool IsFirstInstance()
    {
        mutex = new Mutex(true, "SmartFictitiousApplication");
        return mutex.WaitOne(TimeSpan.Zero, false);
    }
}