It's technically correct. The charity special Doctor Who: The Curse of Fatal Death featured Grant as the Doctor, as well as Jim Broadbent, Richard E. Grant, and Joanna Lumley. The first half of Curse is mostly devoted to the Doctor as he investigates the Master's plans on the planet Tersurus.
We should mention that this was written by Steven Moffat. His greatest contribution to Doctor Who canon was before he got his hands on the TARDIS full-time.
Grant's Doctor made his appearance about 16 minutes into the special, and was born from Broadbent. His first and last act as the Time Lord is to flirt with Emma, only to be shot by a super weapon which is capable of disrupting the Time Lord regeneration process.
Grant's Doctor is meant to be the final Doctor, just another plot point, until the Doctor magically revives from Fatal Death, this time as the first on-screen female Doctor.
It's probably the only time we'll get to see Grant attempt to be the Doctor, even for a short time. It is a good reminder to not take all things into account.
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