// app/AppKernel.php

public function registerBundles()
{
    return array(
        // ...
        new AncaRebeca\FullCalendarBundle\FullCalendarBundle(),
    );
}

// src/AppBundle/Entity/EventCustom.php

<?php

namespace AppBundle\Entity;

use AncaRebeca\FullCalendarBundle\Model\FullCalendarEvent;

class CalendarEvent extends FullCalendarEvent
{
	// Your fields 
}

// src/AppBundle/Listener/LoadDataListener.php

<?php

namespace AppBundle\Listener;

use AncaRebeca\FullCalendarBundle\Model\FullCalendarEvent;
use AppBundle\Entity\CalendarEvent as MyCustomEvent;

class LoadDataListener
{
    /**
     * @param CalendarEvent $calendarEvent
     *
     * @return FullCalendarEvent[]
     */
    public function loadData(CalendarEvent $calendarEvent)
    {
    	 $startDate = $calendarEvent->getStart();
   		 $endDate = $calendarEvent->getEnd();
		 $filters = $calendarEvent->getFilters();
	
    	 //You may want do a custom query to populate the events
    	 
    	 $calendarEvent->addEvent(new MyCustomEvent('Event Title 1', new \DateTime()));
    	 $calendarEvent->addEvent(new MyCustomEvent('Event Title 2', new \DateTime()));
    }
}