As revealed last month, the pair become involved in a huge row after Katy announces she is expecting the baby of older lover Martin Platt. At the height of the argument, Katy grabs a kitchen knife and rams it into Tommy's chest.
Now, in a new twist, Katy - played by Lucy-Jo Hudson - will make an attempt on her own life after police close in on the truth behind the incident. The teenager initially appears to be recovering but "finally dies from complications."
The scenes will be shown in April.