Tyrone (Alan Halsall) and Fiz (Jennie McAlpine) embark on a secret relationship later this month, but it's not long before the pair become careless and Tina spots them kissing passionately.
Knowing that Tyrone's violent fiancée Kirsty Soames (Natalie Gumede) would have a terrible reaction if she discovered the truth, Tina provides her friend with a safe haven to spend time with Fiz in secret.
Keegan told Radio Times: "Tina sees Tyrone kissing Fiz, which obviously is a shock to her. She knew they had a history but that was it. And she thought Tyrone was doting on Kirsty. So it's a shock and maybe a bit of a relief that Tyrone is with Fiz."
The actress continued: "What happens is that Tina becomes their confidante and tries to get them together. So she gives them her flat when she's at work so that they can spend time together.
"She wants them to be together, but she knows that if Kirsty finds out, it wouldn't happen. So she tries to keep it quiet as well."
Tyrone is currently plotting to leave Kirsty, but is only willing to do so after marrying her to secure parental rights over his baby daughter Ruby.
Coronation Street continues tonight (December 10) at 7.30pm and 8.30pm on ITV1.