The 59-year-old actor appeared in the audition to play Starfleet officer Benjamin Sisko in the popular sci-fi series, reported DigitalSpy.
A documentary about "Deep Space Nine" is currently in production and a tweet from the official DS9 documentary account put out the notes from a UK casting session featuring Capaldi's name.
This was followed by the handle releasing images of him and "Merlin" star Anthony Head auditioning for roles.
"Believe it or not, we've seen the audition footage. And it's awesome. #PeterCapaldi #DS9
The role eventually went to actor Avery Brooks.
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