Add a link to the original Facebook event from an imported event listing

link_to_fb_event.php

<?php

/*
 * Add a link to the Facebook event pages right before the content
 */
function tribe_link_to_fb_event() {

	// Check if the event is associated with a Facebook event
	$fbid = tribe_get_event_meta( get_the_ID(), '_FacebookID' );
	if ( empty( $fbid ) ) return;

	// Form and display a link to the FB event page if so
	echo '<p><a href="' . esc_url( "http://facebook.com/events/$fbid/" ) .'" rel="nofollow">See this event on Facebook</a></p>';
}

add_action( 'tribe_events_single_event_before_the_content', 'tribe_link_to_fb_event' );