In another reality, Splinx traveled with a version of the Doctor called "The Wanderer".
Biography
When trying to reset his universe, the Warrior glimpsed into this reality and saw the Wanderer introduce himself and Splinx to a group of people. (AUDIO:The Key to Key to Time)
=Behind the scenes
The casting credits of 'The Key to Key to Time' state that Splinx, along with other uncredited character castings, was voiced by a member of the cast.