Parallel universe (He Jests at Scars...)
From Tardis Wiki, the free Doctor Who reference
In one parallel universe, the Sixth Doctor tried to save the Valeyard from the Fantasy Factory in the Matrix during his trial. As a result, the Valeyard began travelling with Ellie Martin to correct his previous incarnations' mistakes. However, in the process he accidentally killed the Fourth Doctor, erasing himself from history. (AUDIO: He Jests at Scars...)
