ReturnoftheLichKing.com was registered as soon as the title got trademarked four months ago. (some people thought for HS but then proven incorrect) 2) The promotional Year of the Mammoth has Death Knight runes. 3) Hearthpwn datamined an Icecrown image (do a quick google search) 4) Bolvar speaks about a return and a "plan" to take back the Acherus. There are some really huge signs in the DK story alone, however I think it is quite obvious at this point. Return of the Lich King?
I didn't find the right solution from the Internet.