It might be a bit of a spoiler, but it came from Danny Boyle himself, so we also know it to be true. Cillian Murphy will return as Jim in 28 Years Later: The Bone Temple. It appears he'll have somewhat of a cameo reveal, similar to Jack O'Connell's character in 28 Years Later, with more of a role in the third film in the trilogy.
Speaking to Josh Horowitz on the Happy, Sad, Confused podcast, Murphy opened up about what it was like to return as Jim. "I was only on it for a brief period," Murphy confirmed. "But it was quite emotional to go back and to think how bloody long ago it was."
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"The fact that the film still seems to have retained some relevance and people enjoy it still, you know," Murphy continued, before refusing to get involved in any sort of conversation on the third movie, which is still apparently waiting for a green light.
28 Years Later: The Bone Temple arrives on the 16th of January, 2026, and if you want to see more of Jim, you'll have to ensure it's a box office success, it seems.