ae.php

<?php
// bootstrap.php

private function _includes(){
    global $ae_template;
    require_once AE_PRO_PATH.'includes/themes/Ae_Theme_Base.php';
    if(file_exists(AE_PRO_PATH.'includes/themes/'.$ae_template.'/Ae_Theme.php')){
        require_once AE_PRO_PATH.'includes/themes/'.$ae_template.'/Ae_Theme.php';
    }else{
        add_action( 'after_setup_theme', function() {
            do_action( 'ae_external_theme_support' );
        });
    }


   // ... rest of the code
}
?>

// theme functions.php

<?php
add_action('ae_external_theme_support', function() {
  require_once get_template_directory() . '/Ae_Theme.php';
});

?>