UPDATED: 'Doctor Who' season 7.5 spoiler: Who returns, who dies?

Courtesy BBC America
(original version published Oct. 19, 2012. Updated below with statement from Matt Smith)

While visiting Los Angeles, a very reliable source revealed a major spoiler from the upcoming second half of Doctor Who season seven - and it's one that will make Whovians geek out.

To discover, read ahead, but beware - 'thar be spoilers here...

In an episode featuring the children-eating alien race 456 (pronounced four-five-six, and last seen on Torchwood's Children of Earth), the buggers come back and get into a scrap with the 11th Doctor and ... Captain Jack Harkness!

Barrowman, courtesy BBC
In their first on-screen team-up, Matt Smith's Doctor and John Barrowman will face the aliens in a showdown that very well might lead to Harkness' final death.

Although the plot specifics are still a mystery, apparently 456 finds a way to put a limit on Harkness' resurrections and will kill him until the cool cat has no more lives.

What happens then? Will Capt. Jack be dead-dead? Apparently the captain asks that question himself and the alien's reply?

"Spoilers" (Which - coincidentally? - happens to be River Song's catchphrase)

Considering Stephen Moffat's apparent joy in killing characters and torturing fans (and I say that in love), it would not be shocking to see him bump off Harkness. Also, it is about time for Barrowman to appear alongside Smith since both Ninth Doctor Christopher Eccleston and Tenth Doctor David Tennant have adventured with the former Time Agent.

The 456, courtesy TARDIS Index Files
When we last saw Captain Jack, he had regained his immortality after the events of Miracle Day. And the three-headed insectoid 456 (named for the frequency they use to communicate with humans) is a perfect nemesis for Harkness. He has a long history with the aliens, and they were eventually defeated by the Torchwood leader, but only because he sacrificed his own grandson to do so - after they killed his romantic interest Ianto Jones (Gareth David-Lloyd).

In a way, the 456 are Harkness' Daleks. I predict that Jack will have to die in order to save the good Doctor, which is kind of a recurring theme between the two time travelers. And while I couldn't find out when in the second half of season seven this will occur, it sounds like a great finale, don't you think?

And...React! Happy to see Jack back? Are you excited to see him team up with Matt Smith? Think Moffat will really kill him off?

UPDATED Dec. 24, 2012

During an interview Matt Smith has denied filming with Barrowman. Our source still stand firms by the assumption. Here's Smith's statement.
"No. That’s a complete fabrication ... Me and John have never, ever stepped on a film set together. No Captain Jack, as of yet, I’m afraid. No. I would welcome the Captain, you know? He’s The Doctor’s pal. I’m sure John would like to like to come back, but it’s … you’ve got to fly those one’s with Moffat, I’m afraid. I just turn up and try and get the lines in the right order. [laughs]"