In the show, pregnant Steph Scully (Carla Bonner) has entered into a pretend romance with Toadie Rebecchi (Ryan Moloney) to hide the fact that Dan Fitzgerald (Brett Tucker) is the father of her child.
The truth would have repercussions for many characters, including Dan's ex and Steph's good friend Libby Kennedy (Kym Valentine) and mechanic Lucas Fitzgerald (Scott Major), who is the true object of Steph's affections.
Alan, who plays Libby's dad Karl Kennedy, said: "This is a story that's not going to be treated lightly. It's going to be quite a long story arc, and we are waiting with bated breath for when all secrets are revealed because it will tear the street right down the middle."
He said the culmination of the plot will play a part in the soap's ongoing 25th anniversary celebrations.
"All this will coincide with the 6,000th episode which we film in middle of the year. The producers are very serious about making the 25th anniversary year one of the most memorable in the show's history."