Before the Islamic State stormed onto the scene, they were the strongest insurgent group in Syria.

Now, Ahrar al Sham, which means the "Liberators of Damascus" are fighting both the Syrian Army and Islamic State militants.

This week, the group confirmed reports that their leader al-Sheikh Hassan Aboud, seen here, is dead.

A spokesperson says dozens of the group's leaders had gathered in a fortified bunker when there was an explosion. It isn't clear whether an outside party is responsible. Some have speculated a gas attack.

Doctors examining the victims' bodies say they were few external signs of injury, according to images posted to a social media website whose content Reuters cannot independently verify.

The group also announced that Hashim al-Sheikh Abu Jaber will lead the group, along with a new military commander.

While it's too early to know what impact they may have on the fight, what is clear is that the group has no plans to play second fiddl