Here is the solution: Invoke the UnLoaded event of WebView - webView.Unloaded += webView_UnLoaded;
Then change the source of the webview in webView_UnLoaded event handler: Here is my code:
private void webView_UnLoaded(object sender, RoutedEventArgs e)
{
WebView webView = (WebView)sender;
webView.Source = new Uri(" ");
}