The character (played by Harry Visinoni) is currently recovering in hospital after knocking himself unconscious and injuring his head after falling off a ladder.
However, his mother Abi Franklin (Sally Carman) broke the shocking news that he may be HIV positive after doctors concerns grew for his low white blood cell count.
Abi confessed to his girlfriend Faye's (Ellie Leach) mum Anna Windass (Debbie Rush) that Seb might have contracted HIV from an ex-girlfriend.
Anna is now scared that Faye might also be HIV positive and wants her to go and get checked.
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Coronation Street's most dramatic moments
Fri, June 2, 2017
Coronation Street's most dramatic moments.
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Anna Windass wants you dead. She pushed you off that ladder!
Pat Phelan (played by Connor McIntyre)
The Terrence Higgins Trust praised the soap on social media following the broadcast.
The charity, which campaigns and provides services relating to HIV and sexual health, thanked ITV for their “sensitive handling” of the subject.
They posted: “‘HIV doesn't kill anymore, not if it's treated right!' Great to see ITV Corrie handling HIV sensitively.”
It comes as Pat Phelan (Connor McIntyre) lied to Seb and tricked him into thinking it was Anna who pushed him from the ladder.
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Coronation Street's most dramatic exits
Sat, June 10, 2017
We take a look at some of Coronation Street's most dramatic exits
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Shona Ramsey left the street after confessing that she is Clayton’s mum
As Seb lay lifeless and unresponsive at the start of the episode, the villain told him: “Seb, Seb. Hey, take it easy buddy. You gave us a terrible fright.”
He then lurched forward and said in Seb’s ear that Anna was behind his injuries as she “wants him dead”.
He continued: “Anna Windass hates you. She wants you dead. You hear me? Anna Windass wants you dead. She pushed you off that ladder!”