Hi TaintedLove. The speculation is that it will be Alf's late (first) wife, & Roo's mum, Martha & she will be played by actress Belinda Giblin. This rumour started when a fan spotted the following on Belinda's resume on showcast.com.au (it is the 5th one down on her list of 2017 credits):
http://www.showcast.com.au/showcast/...MHeY-KTFDOpCbQ
Considering that the character of Martha Stewart was supposed to have died in 1985 ie 3 years before the show even started in 1988 (& accordingly she was never seen on screen), if it
is true that Martha will make a guest appearance at some stage, I am wondering whether maybe it will just be in Alf's dreams or a figment of his imagination etc? In the trailer for 2018 we see Alf unconscious at the bottom of a hole after a supposed gas explosion, so maybe Martha appears to him in his dreams or something similar, while he is unconscious??
Of course the rumour mill is throwing up a few theories like maybe she faked her death or she was in witness protection or even that this is all just a hoax! I think someone has even mentioned that as Martha was supposed to have drowned, maybe she is still alive & had lost her memory (not another Dee type situation like Neighbours!!). This all seems over the top to me, so if she does happen to return, I think the theory that Alf will just somehow imagine her seems the most plausible. But you really never know these days do you!! We will have to wait & see....
(N.B. Just to be clear, this character of Martha being rumoured to return is Alf's late first wife & Roo's mum - NOT Roo's daughter Martha who was played by Jodi Anasta (who presently plays Elly on Neighbours))