Beware of season 8 spoilers.
Equestria Daily recently broke the news that Mark Acheson leaked his role in season 8, reprising his role as Tirek. Although Equestria Daily was not able to find the original screen shot, bronies have managed to dig up the original post, which Acheson posted on a very small Facebook page for actors back in September. Link below.
Although Acheson’s Facebook page is not verified, it was created in 2010 with many personal pictures of Acheson and not all entertainment personalities have verified Facebook pages.
Judging by the size of the group in which he made his announcement, he might not have meant for anyone to see this information aside from his friends.