John Barrowman had a very special Doctor Who codename to keep his return a surprise

But how did they keep this secret cameo under wraps? Well, speaking exclusively to RadioTimes.com, Barrowman has revealed that to keep his arrival in the story off the radar the Who production team assigned him a secret codename, which was inspired by his former series co-star Billie Piper.

“I had a codename,” Barrowman told us.

“Funnily enough I can't remember what the codename was but I think they can tell you from the script – oh yes, my codename was an anagram of Rose Tyler.”

Cleverly, this codename (the specifics of which the Doctor Who production team are currently keeping under wraps) does tie Barrowman to his earlier appearances on Who – from 2005 he starred regularly alongside Billie Piper’s companion Rose – without directing referencing his character, meaning that even anyone who spotted it at the time was unlikely to join the dots and discover Captain Jack’s return.

And according to Barrowman the unscrambled codename (which we’re currently banking on being something like Roy Lester, Rory Steel, Errol Stye, Terry Leos, Les Torrey or something even more out there) was actually printed on his script, and ended up becoming something of a nickname on set.

https://www.youtube.com/watch?v=kIFIsln9DHY&t=1s

“When we were filming, people were even calling me the name of the character - the Rose Tyler anagram,” Barrowman recalled.

“And I'm like, can we just put 'Captain Jack' in it?”

Arguably that might have been a little less secretive, so perhaps it’s no bad thing that Barrowman didn’t get his wish. Though from now on, we’ll definitely be keeping our eyes peeled for any other sneaky jumbled-up character names that might crop up during Doctor Who filming.

That is, once we’ve stopped having fun coming up with Rose Tyler anagrams. Troy Leers, anyone?

Doctor Who continues on BBC One on Sundays