From the strategy guide...
[spoiler][url]http://i2.wp.com/destinynews.net/wp-content/uploads/2014/09/11-zB3tclw.jpg[/url][/spoiler]
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Calm down. Its a cutscene Its the Sword of Crota http://www.bungie.net/en/Grimoire/2/4611686018428808889/Activities/StoryMoonOceanofStorms