Anonymous source(s) over at TFW says that The Fallen (with a capital "T") is a new character in Revenge, not the same one who appeared in Dreamwave's "Transformers War Within: The Dark Ages" comics, nor any of the previous Decepticons in the first film. However, until Hasbro, Paramount, Dreamworks, and/or other PR folks affiliated with the involved companies confirms/denies it, it's best to take this with a grain of salt.

See the post here at TFW.