Doctor Who has already hinted at how Jodie Whittaker's 13th Doctor will regenerate, and it might be a result of excess memories. The former Broadchurch star took on the role of the iconic Time Lord in 2017, in turn becoming the first female actor to play the Doctor in a leading capacity. Now, her time on the BBC flagship series is coming to a close, with Sex Education star Ncuti Gatwa set to take over.
Jodie Whittaker will bid farewell to the 13th Doctor in an upcoming feature-length special, set to air fall 2022 as part of the BBC's centenary celebrations. Alongside the Daleks and Cybermen, returning for the occasion is Sacha Dhawan's psychotic incarnation of the Master, who pulverized the Time Lords' home planet upon learning about the mythical Timeless Child and its true identity. As per the season 12 finale, the Doctor is the Timeless Child; an otherworldly regenerative being from whom Gallifreyans gene-spliced the ability to regenerate, thus becoming Time Lords. Eventually adopting the title "The Doctor," the child was stripped of their memories by the pioneering Tecteun, leaving the heroic Time Lord introduced to audiences in 1963 none the wiser about their former lives.
Season 13, episode 5, "Survivors of the Flux," sees the 13th Doctor reunited with Tecteun, the merciless Gallifreyan scientist who happened upon the mysterious Timeless Child beneath a dimensional boundary. Before perishing at the hand of Ravager Swarm, Tecteun tempts this version of the Doctor into regaining her stolen memories by opening a chameleon arch in the form of a fob watch. Naturally, she doesn't submit to Tecteun's offer and instead pockets the device, depositing it deep within the TARDIS after saving the universe from the destructive flux energy. For now, the contents of the chameleon arch remain a mystery to both audiences and the Time Lord herself, though it's more than likely that the centenary special will see the 13th Doctor finally open the watch. It could be this overwhelming surge of knowledge about her long-lost selves that leads to her climatic regeneration. Or Tecteun could have rigged the arch with an in-built trap; if the Doctor indulges in her past memories, she will be forced to regenerate.
Winding back, before using a Passenger form to absorb the flux energy, the Doctor faces an ancient being that claims to be the embodiment of time itself. It presents the Doctor with an ominous prophecy. "Your time is heading to its end. Nothing is forever. No regeneration, no life. Beware of the forces that mass against you… and their master." Of course, Time is suggesting that the Master will ultimately be responsible for bringing about the 13th Doctor's death. Perhaps the Master forms an alliance with the Daleks and the Cybermen, and together they wreak havoc upon Earth; the Master promises to call a ceasefire if the Doctor opens the fob watch, and the sudden storm of knowledge or influx of energy that ensues consequently results in her regeneration, and maybe the Master's too. This would be fitting, given that the Master is hell-bent on discovering the truth about the Timeless Child. He would die to attain that knowledge.
Until more information is released, audiences can only speculate as to how Jodie Whittaker's Doctor will face her demise. Jamie Magnus Stone, the director of the currently untitled centenary special, revealed (via Digital Spy) that the 13th Doctor will regenerate outside of the TARDIS for the first time in recent history. Additionally, footage from the special glimpsed at the end of "Legend Of The Sea Devils" teased a scene depicting a regenerating Doctor screaming for Yaz while encased within a holding cell. This, however, is likely a fake-out, or merely the beginning of the regenerative process. Either way, Jodie Whittaker's time on Doctor Who is sadly coming to an end this fall.