Original Third Doctor

An incarnation of the Doctor was seen during the Fourth Doctor's mindbending contest with Morbius. (TV: The Brain of Morbius, AUDIO: Cold Fusion) According to one account this man was an incarnation of the Other, whom the First Doctor was a reincarnation. (PROSE: Lungbarrow)

After Patience was widowed by Omega, she became the Doctor's tutor, as she had been his father's and grandfather's. They fell in love and had thirteen children. Some of them likely in this incarnation. (PROSE: Cold Fusion)

behind the scenes
The face of this Doctor were first introduced in TV: The Brain of Morbius but it was not until AUDIO: Cold Fusion thirty years later, in 2016 thatthey were confirmed to be incarnations of the Doctor.