Doctor Who season 6 very nearly saw the immortal Captain Jack Harkness cross paths with Matt Smith's 11th Doctor for the first time. Prior to his own Doctor Who spin-off in the form of Torchwood, John Barrowman first played the enigmatic Time Agent Jack Harkness during Christopher Eccleston's short-lived tenure as the Doctor in 2005. After returning to the show for several episodes throughout David Tennant's run as the titular Time Lord, Barrowman's last Doctor Who appearance before his intended return in season 6 was during the 2010 New Year's Day special, "The End of Time: Part Two," which bid farwell to the 10th Doctor.
Season 6, episode 7, "A Good Man Goes To War," sees Matt Smith's 11th Doctor raise an army against the captors of Amy Pond and her baby, led by the eyepatch-clad Madam Kovarian who intends to weaponize the child against the Doctor. The Time Lord's makeshift army is a menagerie of his greatest allies. At one point, showrunner Steven Moffat had intended to dip into the pool of characters introduced during his predecessor Russell T Davies' run rather than limiting himself to new, more original creations to form this army, as seen in the aired episode. This almost led to the 11th Doctor calling upon Captain Jack Harkness to fight in the Battle of Demons Run; the Doctor's darkest hour.
Ultimately, plans to revive the character of Captain Jack were derailed when it became apparent that actor John Barrowman would not be available for filming during the winter of 2010. Barrowman was busy leading the cast of Torchwood: Miracle Day, season 4 of the adult-oriented Doctor Who spin-off which was based in America for the first time. This made it impossible for the star to travel to Cardiff to film the material necessary for "A Good Man Goes To War," Steven Moffat revealed (via TV Line) in a 2011 interview. “Even if he was doing the role in Wales, that's really hard to do,” explained the showrunner. Fans at the time expressed their disappointment upon hearing this revelation, as Captain Jack is naturally by the Doctor's side whenever he's in need of assistance. All things considered, it's a shame that Barrowman's hectic filming schedule didn't permit Moffat's plans to come to fruition, as an appearance from Captain Jack would've greatly complimented the already spectacular story.
Will Jack Harkness Meet The 14th Doctor?
A decade after his cameo in David Tennant's swansong story, Moffat's successor Chris Chibnall finally elected to unite Captain Jack with Jodie Whittaker's 13th Doctor at the tail end of season 12. Barrowman and Whittaker sparked great chemistry together on screen as they vanquished the Daleks. Undoubtedly, Smith and Barrowman would've been an equally as electric double act had the character returned during season 6. After all, the storyline presented in "A Good Man Goes To War" set the stage perfectly for Captain Jack's return, which in turn would've created a greater sense of continuity within the Doctor Who universe. A true marriage of eras.
As Russell T Davies prepares for his return as showrunner in time for Doctor Who's highly-anticipated 60th anniversary and seasons beyond, it seems unlikely Captain Jack Harkness will ever meet the 14th Doctor. This is due to resurfaced reports of the actor's sexual misconduct during Davies' original run on the revived series. Though the controversial actor almost reprised his fan-favorite role for Matt Smith's 2nd season as the Doctor before donning the trench coat once again in 2020, perhaps a period of reflection and a properly served apology would be best for John Barrowman if he wishes to return to Doctor Who in the future.