This has been rumoured since 2011 before Kat and Alfie got Tommy back from Ronnie. There was some talk that the fact that a DNA test needed to take place in order for them to get Tommy back would lead to the reveal, although I never understood that as presumably Alfie wouldn't have been tested because they thought he wasn't the father. Once we discovered that Alfie wasn't infertile, this was rumoured more and more, which led to Bryan Kirkwood confirming (in an interview) that Michael was the real father. Now that he's gone, some hope that Lorraine Newman or another executive producer will reveal Alfie as the father, given that there was never any medical evidence to say that Michael is the father. Some have even picked up on the amount of times that Tommy seems to be ill, and wonder if this is leading to an organ donation or blood transfusion storyline. It has been reported as well that Jessie and Shane believe that Tommy is Alfie's.