Close winforms application with mainform hidden

I am trying to close my winforms application through the Form.Closing event, with a custom message (Do you want to exit yes/no). For this I have edited the onFormClosing event for every form in my c# project. Like so:

protected override void OnFormClosing(FormClosingEventArgs e)
{
    base.OnFormClosing(e);

    if (e.CloseReason == CloseReason.WindowsShutDown) return;

    // Confirm user wants to close
    switch (MessageBox.Show(this, "Are you sure you want to close?", "Closing", MessageBoxButtons.YesNo))
    {
    case DialogResult.No:
        e.Cancel = true;
        break;
    default:
        break;
    }        
}

When the user clicks Yes, I want to get the entire application to exit. However, I have a main form which functions as a loginform. When the user logs in, the mainform gets hidden and a different form displays.

So when the user clicks Yes, the entire application does not end, because of that hidden form. How can I make sure that the entire application gets shut down?

I have tried Application.Exit(), this fires the messagebox confirming the shutdown again, because it calls the OnFormClosing event.