Doctor Who’s showrunner Chris Chibnall has upheld Steven Moffat’s recton of a significant Time Lord ability – which was introduced by their predecessor, Russell T. Davies. As audiences have learned more about the heroic Doctor’s mysterious past, the show’s many writers have also detailed what characterizes the denizens of Gallifrey over the course of Doctor Who’s long history. Along with the power of regeneration and their superior intellects, Time Lords are also telepathic, perfectly adapted to time travel and, thanks to their physiology, they are considerably more durable than humans.

Yet while most of these qualities have endured across the sci-fi show’s many seasons, one of the newest Time Lord powers has been conspicuously dismissed in Doctor Who’s most recent episodes. At the climax of “Spyfall: Part 1”, viewers were dealt a shocking twist. In their campaign against the Kasaavin, the Thirteenth Doctor (Jodie Whitaker) and her crew have been aided by the kindly and mild-mannered Agent O (Sacha Dhawan). But in a stunning development, O is revealed to be the Doctor’s archenemy, the Master. Thanks to the Master’s new regeneration (and his talent for deception) the Doctor was unable to recognize him; but according to an earlier episode, the Doctor should have been able to seen past O’s disguise.

Indeed, in one of Russell T. Davies most famous arcs, he denoted that Time Lords could always detect fellows of their species, even after a change in appearance. Though this deductive skill had been subtly implied in one of the Fourth Doctor’s (Tom Baker) stories, it was first properly introduced in the season 3 episode “The Sound of Drums”. Picking up shortly after the Master (John Simm) has regenerated and escaped to Earth, leaving the Tenth Doctor (David Tennant), Martha Jones (Freema Agyeman), and Jack Harkness (John Barrowman) stranded in the far future, when the trio land in 2007 - hot in pursuit - Martha laments that the Master could be almost impossible to locate due to his transformation, which they failed to observe. However, the Doctor replies that this won’t be an issue, and he explains that Time Lords can recognize each other through sight alone. Indeed, the Doctor demonstrates this ability mere moments later when he spots the new British Prime Minister, Harold Saxon, on TV and correctly confirms his true identity.

This supernatural awareness was later expanded upon at the very end of Davies era where, during their wasteland confrontations in “The End of Time”, the two rivals were implied to even feel when the other was nearby. Yet this was not to last, since Steven Moffat retconned this trait out of existence during his tenure as Doctor Who’s lead writer. When the Twelfth Doctor (Peter Capaldi) came face to face with Missy (Michelle Gomez) for the first time in the season 8 finale, he was oblivious to the fact that she was the Master in female form. As such, the case of the Thirteenth Doctor and Agent O confirms the stance of Doctor Who canon: Time Lords cannot detect each other across their regenerations.

Fans may lament the loss of this quirky power for the Doctor and her race, yet in many ways, this amendment is completely understandable. Doctor Who thrives on the mystique of the Time Lords, as well as their ability to reinvent themselves in new and unpredictable ways. This reset button inherent to the show has been key to its longstanding success. Therefore, if many of Doctor Who’s main characters can recognize each other through a single glance, this detracts from the show’s unknowability – and robs audiences of the kind of dramatic reveals that occur in “Dark Water” and “Spyfall”, which have become fan favorite moments of the show.

Therefore, unless Chibnall or his successors choose to walk back on this retcon, Time Lords will no longer be able to recognize each other across their regenerations, meaning that the irregularity of “The Sound of Drums” looks set to become one of the endearing, canonical inconsistencies that Doctor Who is famous for.

More: Who Is The Timeless Child? Doctor Who Season 12’s Big Mystery Explained