How to hide Gtk Popup Window when user clickes outside the window

I have developed one popup window (Non decorated) using GTK+ and glade tool in C. It popup on its parent window when a button clicked. I want to destroy or hide this popup window when user clicks out side this window. User can click on parent window or any other window. I have tried to capture GDK_FOCUS_CHANGE event but I am not able to capture this event. Is there any way to achieve this? How do I know that click is on other window then pop up window? How is it clear that pop up window has lost it's focus? So that I can hide it. The relevant code is as follow:

/*
 * Compile me with:

 gcc -o popup popup.c $(pkg-config --cflags --libs gtk+-2.0 gmodule-2.0)
*/

#include <gtk/gtk.h>

static void on_popup_clicked (GtkButton*, GtkWidget*);
static gboolean on_popup_window_event(GtkWidget*, GdkEventExpose*);

int main (int argc, char *argv[])
{
    GtkWidget *window, *button, *vbox;

    gtk_init (&argc, &argv);

    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title (GTK_WINDOW (window), "Parent window");
    gtk_container_set_border_width (GTK_CONTAINER (window), 10);
    gtk_widget_set_size_request (window, 300, 300);
    gtk_window_set_position (GTK_WINDOW (window),GTK_WIN_POS_CENTER);

    button = gtk_button_new_with_label("Pop Up");
    g_signal_connect (G_OBJECT (button), "clicked",G_CALLBACK (on_popup_clicked),(gpointer) window);

    vbox = gtk_vbox_new (FALSE, 3);
    gtk_box_pack_end(GTK_BOX (vbox), button, FALSE, FALSE, 5);
    gtk_container_add (GTK_CONTAINER (window), vbox);

    gtk_widget_show_all (window);
    gtk_main ();
    return 0;
}

void on_popup_clicked (GtkButton* button, GtkWidget* pWindow)
{
    GtkWidget *popup_window;
    popup_window = gtk_window_new (GTK_WINDOW_POPUP);
    gtk_window_set_title (GTK_WINDOW (popup_window), "Pop Up window");
    gtk_container_set_border_width (GTK_CONTAINER (popup_window), 10);
    gtk_window_set_resizable(GTK_WINDOW (popup_window), FALSE)