You are correct; it's in the Hitchhiker's Guide entry on Professor Enigma (here). But you've remembered correctly in the particulars, anyway.

>Essentially, the way it goes is that the Professor was and always had
>been male, but during the lead-up to the regeneration from the 99th
>Professor to the 100th, the BBC were running a big teaser-style "wait
>till you see what's we're going to do to mark the Big Significant
>Number" build-up-the-anticipation promotion/hype campaign.

It was the show's most successful pre-series promotional campaign ever! The tagline was, "Professor Enigma: Like No Other."

>And the whole of her reaction, when she noticed the change, appears to
>have been to say "Okay. That's different." and take it entirely in
>stride, carrying on completely as normal. (Or as normal as things ever
>are after a regeneration, anyway.)

Her post-regeneration psychosis involved not believing people when they told her she was a woman, having been far too busy to take inventory. This went on until she caught sight of herself in a reflective surface and said, "Wait, stop the press, who is that? And why is she wearing my clothes?"

Once she'd snapped out of that, though? Yeah, business as usual.

As an aside, the bit at the end of the Guide file about the rumors that she was only going to stay for one season? Not true, but you know the Guide. The reason the producers didn't explicitly confirm that she'd be staying was because they were hedging their bets against the possibility that the Doctor would screw up during the off-season and cause her to miss 2410 or something. They had a rather clever contingency plan in place for that (not just a face-unseen regeneration like the one at the beginning of "Time and the Rani"), but it turned out not to be necessary. Instead, they just had to explain why she's suddenly become 30ish, which was much easier to dispose of in the first episode of series 424. :)

--G.
"That's you, Professor." "Is it? Oh! That explains a lot of things, actually. Well, come on, John. Don't just stand there basking in my pulchritude, work to do."
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Benjamin D. Hutchins, Co-Founder, Editor-in-Chief, & Forum Admin
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