Looking at the spoilers for this week, I think we'll probably be lead to believe it's Pete Beale and that's what Sharon will believe but it will turn out to be someone else.
I think it might be Les. It makes sense if you think about it, he's already proved that he's got secrets, it would also explain the letters that her biological dad sent, asking about her as obviously he's only moved onto the square recently and wouldn't know Sharon was his daughter. Plus Pam used to be a social worker so i'm sure in true Eastenders fashion it'll probably turn out she was involved in some way.
All it takes for the solicitor to bump into Pam and she'll realise that Sharons real dad lives just around the corner from her.
Les makes more sense than any characters from back in the day as obviously if it's an old character, it creates a big plot hole in the fact that the dad wrote to ask about her and why would they do that if he was living right on the square?
It's either that or Kathy's husband Gavin but I think that's one plot twist too far. How and why Kathy's come back from the dead after all these years plus reuniting with her two sons are bigger storylines than a twist that her husband is Sharons' dad.
They uncharacteristically released quite a lot of details about this plot which makes me think some of them are red herrings and there are going to be more twists and turns. I highly doubt we'll actually discover who Sharons dad is next week!
Either way, I'm really enjoying this plot. It's certainly quite a twist on your usual 'who's the daddy' storyline! lol