In an article containing an interview with actor Sacha Dhawan, it is revealed in Doctor Who Magazine 582 that the fatal event that causes the thirteenth Doctor to regenerate is likely a personal battle between the Doctor (Jodie Whittaker) and the Master (Sacha Dhawan). Interviewer and DWM writer Paul Kirkley hints at the scene,

“There’s one pivotal, jaw-dropping moment in the episode — no spoilers, but you’ll know it when you see it — that Sacha Dhawan is particularly proud of.”

“When the great Terrance Dicks first proposed the character of the Master to producer Barry Letts more than half a century ago, he famously sold him as ‘the Moriarty to the Doctor’s Holmes’. So it’s fitting that Sacha’s Master and Jodie’s Doctor should face each other in their own ‘Reichenbach Falls’ moment.”

“I wanted it to be epic and moving, and when I watched the episode myself, I thought, ‘I’m so glad we landed that’,” Sacha Dhawan told Kirkley. “Because it kind of takes your breath away a bit.”

“So it’s always been really easy with Jodie. I do my thing and she does hers, and it just works. And that’s because, even though the characters have so much animosity between them, me and Jodie really adore each other. Which actually makes the scenes much more electrifying, and a lot more moving than I thought they would be. Especially in the Centenary Special. I watched the episode on my laptop in a dark room the other day, and I was just a blubbering mess.”

Reichenbach Falls refers to a scene in the Sherlock Holmes adventure The Final Problem, in which Sherlock Holmes’ friend Dr. Watson believes Holmes and his arch-enemy Professor James Moriarty have fallen to their deaths in an epic hand-to-hand battle on a precipice overlooking Switzerland’s Reichenbach Falls over the deep chasm containing the falls.

The combat is depicted in Sidney Paget’s 1893 illustration of the adventure The Strand Magazine.

There are rumours that the thirteenth Doctor’s demise will occur in a fall off of a cliff and there was some filming in a quarry with steep sides during the filming of The Power of the Doctor.

I’m not saying where I found this but since Mandip Gill is in her centenary special costume, I suspect this was taken at the filming at the quarry in Bridgend on either October 7 or 8. By the way, does anyone know which quarry they used? #dwsr pic.twitter.com/U28sKciBef

— Doctor Who Production News (@DoctorWhoPN) October 18, 2021

The Power of the Doctor is confirmed to air some time in October during the BBC’s week-long celebration of the October 18 centenary of their charter.

BBC America typically runs a Doctor Who marathon leading up to a Doctor Who special and, according to their schedule, there is no such marathon in the week prior to the BBC’s centenary week so BBC One and BBC America will likely transmit the 90-minute spectacular later in the week, likely on October 23 as part of a BBC week-long celebration.

Doctor Who Magazine 582 includes a The Power of the Doctor preview including interviews with Sacha Dhawan, Janet Fielding, Sophie Aldred, Patrick O’Kane and Ray Holman. It is available at newsstands in the UK and by digital issue on Thursday, September 15.