A short teaser video with the tag line "He Has Returned" is currently circulating on the LoL social media accounts! The short video shows what appears to be Pantheon gazing into the night sky.
While it is speculation, the scene from the video seems to follow the last part from Pantheon's "The Spear of Targon" story as well as the sky described in "The Aspects".
Click here for more on Mount Targon: http://na.leagueoflegends.com/en/site/mount-targon/