Doctor Yes's universe
One parallel universe existed alongside that of Doctor Doctor. It was home to Doctor Yes, Patient 2, and AIEI-OHYEAH, who "solve[d] problems across the galaxy and saved whole planets from disaster", according to Patient 2.
Doctor Yes was aware of an individual called "Dr Who". Despite apparently being from a "parallel universe", Yes claimed that they were from a more advanced ship "light years away".
History
Aboard the STARSHED, Doctor Doctor once accidentally opened a portal into this universe, dubbed by AIEIO as "a parallel universe". As a result of this, Doctor Yes, Patient 2, and AIEI-OHYEAH - this universe's counterparts of Doctor Doctor, Patience Patience, and AIEIO - appeared in the STARSHED shower. Yes soon deduced that they were alternate versions of each other, noting that "some wally" had opened a portal into a parallel universe.
When the STARSHED crew's counterparts began to close the portal, AIEIO told them that they should go back through and return to their universe, but Doctor Yes suggested that they could stay in Doctor Doctor's universe, living together in the STARSHED, an idea the STARSHED's crew were displeased with. The crew of the STARSHED then tricked their counterparts into entering the shower to clean it, sending them "down the chute". (TV: Double Trouble! [+]Loading...["Double Trouble! (TV story)"])
Behind the scenes
It is unclear if a version of the Doctor exists in this universe, or if Doctor Yes is simply aware of a version of them, possibly that of the conventional Doctor Who universe.
