‘Torchwood’ star John Barrowman feels that the sci-fi series and its sister show ‘Doctor Who’ have developed separate identities and that ‘Torchwood’ is no mere spin-off.

"You know, every year ‘Torchwood’ has become something a little different than it was before,” he told New York magazine. “It's still sci-fi, but it doesn't just deal with spaceships and aliens all the time, because we've done that. Our science fiction is more psychological.

"Our sister show, ‘Doctor Who’, is the one that does that: talking cats and Cybermen and Daleks - which is brilliant, but we're something completely different now."

Barrowman's character Captain Jack Harkness first appeared in ‘Doctor Who’ in 2005. Since Captain Jack has become central to ‘Torchwood’, but has also returned for guest appearances on ‘Doctor Who’.

Barrowman further suggested that he never worries about Captain Jack being killed off by Torchwood's creators because it was already revealed in a 2007 Doctor Who episode that he will ultimately become the aged Face of Boe.

"There couldn't be a ‘Torchwood’ without Captain Jack,” he maintains. “That's the bottom line. If the time comes when it's time for him to leave - they couldn't kill him. They have to wait until he's the Face of Boe before he dies.”

'Torchwood: Miracle Day' premieres on Thursday, July 14 on BBC One.