"Russell wanted that to happen, although they are my words," he said. "It was absolutely the right thing to do, though, from the point of view of the story and what it gave to the last episode.
"The strength of Torchwood and Russell's vision is that you don't know the heroes are going to survive. That's been well established now!
"That adds a sense of jeopardy to the show which leaves everyone wondering what will happen next."
For the writer, Ianto's death was a means to show the cost of immortality for Captain Jack Harkness: a character who could only live to see everyone else ultimately die around him:
"In my mind, I was always aware that Jack had gone through this situation many times before, and that was really interesting to me. How do you have a relationship and fall in love with someone when you know -- absolutely know -- you will be around to see them die?
"That's a real tragedy that Jack has to carry around with him, as well as a fascinating weight to hang around a character's shoulders."
When Fay was asked if he planned to bring Ianto Jones back to the series, the writer answered: "I'm not going to answer that [...], you'll just have to watch and see."