In a dramatic turn of events for the soap's Halloween episode, Silas had a terrifying showdown with Lynsey Nolan (Karen Hassan) and vowed to kill her - pointing out that it was the only way anyone would ever believe her accusations against him.
When Lynsey managed to escape, Silas (Jeff Rawle) was in hot pursuit but made a catastrophic error when he confused Heidi with Lynsey due to their identical Catwoman costumes. After striking again, Silas was left devastated when he realised that he had killed his own flesh and blood.
In real life, meanwhile, actress Kim Tiddy decided to bow out from Hollyoaks for pastures new earlier this year. Here, Kim chats exclusively to Digital Spy about her decision and Heidi's shock exit.
Why did you decide to leave Hollyoaks?
"I've really enjoyed playing Heidi and I've loved my time in Liverpool, but after a year and a half, I felt like it was time to move on."
What did you think of Heidi's shock exit storyline?
"I thought the storyline was fantastic! I was also killed off in The Bill, and I'm taking it as a compliment as I think shows like to kill off likeable and popular characters. I can obviously die really well!"
What was it like to film the exit scenes?
"It was very high drama - I loved the whole Halloween theme and the fact that it was shot at night. It was exciting to film and to get dressed up as Catwoman! I also think the storyline leading up to it was very clever, and the twist at the end where Silas killed Heidi was great."
What has Jeff Rawle been like to work with over the past year?
"He was fantastic. Unfortunately, I didn't get as many scenes with him as I might have liked, but he's such a well-established and experienced actor with a great wealth of knowledge. He's been a great asset to the Hollyoaks cast. He's very professional, funny and kind - if you ask him a question about his career, he's always very open. I know a lot of the younger actors feel the same way about him. I'm very proud to have worked with him."
How do you think Silas will cope with what he's done?
"I think he wouldn't have a heart if it didn't affect him in some way. I think we'll see some remorse from him, as killing Heidi was a genuine mistake, and that's what is so great about the storyline. I hope we see some remorse!"
Are you hoping that Heidi's death will have a big impact on the Costello family in the long-term?
"Definitely. I think it will, because she's like the matriarch and the figurehead of the family. She's the strength of the family, so I think they'll definitely crumble following the news of her death. But I suppose we'll have to wait and see what happens. Keep watching!"
Did you find it emotional when you said goodbye to your colleagues after filming your last scenes?
"It was emotional, but most of my goodbyes were before my final scenes as I filmed them on a night shoot at around 3am, so there weren't too many people about. I've really enjoyed working at Hollyoaks and I met some really great people - especially the other Costellos, as I really got on well with them. I'll miss them. It's a nice environment to work in, it really is. I'm coming away from the job with lots of fond memories."
Will you be staying in touch with many of the cast?
"Definitely. We have the power of Twitter now and Facebook, which makes it a lot easier to keep in contact with people. With the people who I was closest to, I still call and text them regularly, and that's great. I'm also hoping that I can still see people at parties and events - we can have a good catch-up then."
We know that Victoria Atkin, who plays Jason, is also leaving the show. Do you think she has a bright future ahead of her?
"She definitely does - I think she's done really well playing a very difficult character. It just shows that she can be quite versatile. She's a really, really conscientious young actor - she's worked really hard and she deserves even more success. I wish her all the luck in the world."
Are you proud that you were able to be involved in the transgender storyline?
"Most definitely. It was great, because Hollyoaks helped Victoria to do a lot of research and she was able to meet people who had gone through the same thing. I've also learned about the issue, which is great. I thought it was very well-handled - some great writing for quite a sensitive subject."
Are you also proud of the work that your other screen kids Rob Norbury (Riley) and Miles Higson (Seth) have done recently?
"Yeah, I thought Rob stole the show in the wedding episodes - he was really, really good. Jen Metcalfe did fantastically as well. With Miles, this is his first acting job and he's come on so much. I am quite proud of Miles - he's my little favourite, but don't tell him that! Miles is lovely because he's open to learning. I'd never say, 'You should do it like this' or 'You should do it like that', but Miles was always very open to any advice or suggestions. I thought Miles was great in the wedding episodes as well - that was a really great week for Hollyoaks."
We recently saw Heidi and Carl split, but do you think she would have taken him back eventually?
"Well, there'd been such severe damage done to their marriage, but I really don't know. As Kim, I'd like to say that she wouldn't have taken him back, but I think Heidi just loved Carl way too much. She always had a bit of a blind spot when it came to Carl, so she probably would have taken him back - sadly!"
Mitzeee was the other character who Heidi had a lot of scenes with. Did you enjoy working with Rachel Shenton too?
"Oh yeah, Mitzeee's a great character and Rachel and I are really good friends. I think our two characters had quite a good energy on screen together. Rachel plays Mitzeee brilliantly."
How did Hollyoaks compare to The Bill?
"Well, as I was playing a policewoman on The Bill, the storylines weren't so much about the character's personal life - whereas with Heidi, I was able to explore the personal and family life a lot more. I was playing a mother, so playing Heidi was a lot more varied - and obviously a lot more glamorous! But The Bill will always have a special place in my heart, because it was my first TV job - I was there for four years, I absolutely loved it and I learned so much."
What other highlights can you name from your time at Hollyoaks?
"Well, I got to meet some great people and I had a great time in Liverpool. I'm really glad that I was able to play a range of emotions as Heidi - sometimes she was having a laugh, sometimes she was sobbing and there was a bit of comedy too. I got to work with some really great directors as well, which was brilliant.
"I also loved being part of a family on the show, as I've never really done a TV job or a play where it's been focused on a family before. I thought we all worked really well together. Heidi and Carl had a great energy on screen, and it was the same with myself and Paul [Opacic] in real life. I got on really well with Paul off-screen, and I think that came across on camera as well. It was quite a believable husband and wife relationship.
"But I suppose the main highlight was that it was fun to go into work every day. I know a lot of actors say that, but we're just very lucky to get up and go to a job that we really love doing."
What are your future career plans? Would you like to do more TV work, or perhaps focus on theatre or film?
"I'd like to continue on TV. I really enjoy working on camera. It'd be great to do a film as well, and I do love theatre as that was the basis of training at drama school. I just want a really varied career - I'd love to build my CV up so that it's really varied. I want to build up more experience in the profession."
What would be a dream role for you?
"I really like comedy, so I'd love to do a bit of that. But then I really enjoy stuff like Luther and Waking The Dead as well. My ideal role would be a Prime Suspect Helen Mirren-type character. I've also got this idea that I'd like Midsomer Murders to be a bit modernised - I think the new actor in that is brilliant, but he needs a young, funky sidekick! That could be me!"
How would you like Heidi to be remembered by Hollyoaks fans?
"I'd love her to be remembered as someone who brought a bit of glamour to Hollyoaks. I'd also like her to be remembered as someone who was very strong, loyal, caring and dedicated to her family."
Will you carry on watching the show to see how the Costellos are getting on?
"Yeah, I will! I watched it before I was in it, and I'll most definitely watch it again. You've got to support your mates and the show as well, especially as I'm leaving with such happy memories."
> Read all the latest Hollyoaks spoilers and news
Hollyoaks airs weeknights at 6.30pm on Channel 4, with a first-look screening at 7pm on E4.
Rewatch Hollyoaks' latest Silas twists in the videos below: