GRAPHIC: Jack was just 18 years old when he underwent heart transplant surgery.
Jack: I woke up in London, so it was very confusing. I remember one of the doctors coming in and just saying, “Jack, you’re going to have to have a heart transplant.”
GRAPHIC: When he was younger, Jack was very active and ran in a cross country club.
Jack: Everything had been taken away from me. So, I was used to driving around and doing what I want. And then there I am, strapped in a bed, hooked up to loads of machines, and I don't even have the strength to sit up in bed or get out and walk.
I was very, very determined to get back to how I was, always looking at pictures and videos of myself before. I couldn't stand seeing myself like that. My phone wouldn't even unlock, like from my face ID, it wouldn't even recognise me.
GRAPHIC: One doctor said Jack was the 'poorliest' boy they'd ever seen survive intensive care.
Jack's Mum: We've been back to thank the nurses and the doctors a couple of times, and I've just said, you're just miracle workers, you've given us our son back.
Jack: My thoughts on Harefield is that it's an incredible place. It's absolutely outstanding. It doesn't even feel like a hospital when I'm there. It feels like a second home almost, it's crazy. And all the staff are so nice, they're really kind.
Jack's Mum: They've brought him from basically the brink of death, to being a normal person again, and we just can't thank them enough. It's just absolutely incredible, and our family is complete.