Show bosses first teased that Ally has a dark past some time ago, and fans can expect this to become apparent on screen within the next few weeks.
Speaking on Channel 5's The Wright Stuff this morning (June 6), O'Connor suggested that Ally will no longer seem similar to his Neighbours character Ned Parker, who he played between 2005 and 2008.
Discussing how Ned and Ally's stories crossed over, the actor commented: "I think initially they did. Ally's quite a strait-laced… well, we assume that he's a strait-laced good boy. But that's all about to change!"
O'Connor went on to joke about how Ned and Ally both sparked speculation over their sexuality in their first storylines.
He said: "I think the reason why that came up [on Neighbours] was because [Ned] was very secretive about something, and so everyone assumed that [he] was in the closet. But the fact was that [he] really liked musical theatre and was trying to hide that from everyone else.
"The same sort of thing happened when I started on Hollyoaks. They were trying to work out whether he was gay or straight - Ste and Amy were both vying for his attention. But it turns out he's straight!"
At the weekend, it emerged that Ally will become embroiled in Hollyoaks' Walker storyline in upcoming episodes. When Lynsey Nolan spots Walker threatening Ally to keep quiet over something, she decides to do some detective work and find out what is going on between the pair.
Hollyoaks airs weeknights at 6.30pm on Channel 4, with a first look screening at 7pm on E4.