Leela (Splinters)

After the Last Great Time War, a version of Leela was created by the Spriggan, a malevolent version of the Doctor from another universe.

This Leela, who had believed herself to be the original of the Doctor's universe, helped the Tenth Doctor to defeat the Spriggan. Leaving Leela with the Spriggan's TARDIS, the Doctor suggested that she could chose to rejoin the war and become one with her other self, among other possibilities. (AUDIO: Splinters)