The presence of Doctor Who season 15 cast may be new, the actor playing the incoming companion has already embodied a character within the show's storied history. This is something the show has dealt with before, but it's not always explained, nor is a big deal always made.

After end of Doctor Who season 14, Ncuti Gatwa's Fifteenth Doctor was left without a regular companion in 2024's Christmas special, "Joy to the World." So, as is tradition, someone else is stepping into the TARDIS in season 15 to travel through space and time with the Time Lord. The mystery surrounding the newcomer arguably runs just as deep as it did for Gibson's character at the start of her run, but for very different reasons.

Doctor Who Could've Just Ignored Belinda's Connection To Mundy Flynn, But I'm Glad It Isn't

Both of Sethu's Doctor Who characters are receiving a canonical connection

Varada Sethu stepping in to replace Millie Gibson doesn't mark the former's Doctor Who debut. In fact, both of them starred in season 14's "Boom" alongside Gatwa. However, while Sethu was playing Mundy Flynn in "Boom," season 15 will see her step into the role of Belinda Chandra - the Doctor's new companion. I wouldn't have been too surprised if the show had simply glazed over the fact that Sethu had snagged two Doctor Who roles in such quick succession, but the season 15 trailer has thankfully put my fears to rest in that regard.

Fifteen can be heard telling Belinda, "There is something already connecting us," while showing an image of Mundy on the TARDIS view screen.

In the promotional reel of what's to come in Doctor Who season 15, Fifteen can be heard telling Belinda, "There is something already connecting us," while showing an image of Mundy on the TARDIS view screen. The scene is almost definitely a reference to both actors starring together in "Boom," and I can't imagine it's just a gentle tap on the fourth wall. I'm very excited that Davies is actually choosing to connect both of Sethu's characters, and I genuinely believe that it was his plan from the start, especially given how close together seasons 14 and 15 were made.

Doctor Who Has A Good Track Record Of Explaining Returning Actors

Martha Jones & the Twelfth Doctor have both received retroactive explanations

Varada Sethu is very far from the first Doctor Who actor to have more than one character in the show's canon. For example, Freema Agyeman appeared in Doctor Who season 2 as Adeola Oshodi before being cast as Martha Jones ahead of Doctor Who season 3. I've always taken the lazy-yet-serviceable explanation of them being cousins as a clear sign that this was never part of the plan.

Similarly, Peter Capaldi's three Doctor Who characters were also given a retroactive connection that was likely never intended to be required. So, Varada Sethu playing both Mundy and Belinda could be a refined version of something the franchise has already done countless times. Now, it seems far less like Sethu simply impressed Davies with her performance in "Boom" and was asked to return regardless of the impact on Doctor Who canon. Instead, it seems far more like she was installed in that season 14 episode to plant the seed of Belinda's arc and her connection to the Doctor.

What The Connection Between Belinda & Mundy Flynn Could Be

Clara Oswald could be a loose blueprint for the Belinda/Mundy connection

The closest comparison I can think of when it comes to how Belinda and Mundy could share an in-universe connection is all the versions of Jenna Coleman's Clara Oswald that permeated the Doctor's timeline. Matt Smith's Eleventh Doctor ran into many different characters with Clara's face and similar names, who all seemed to have no knowledge of one another, after she was scattered throughout various points in Eleven's life. Written by Steven Moffat, the Eleven/Clara arc could have influenced Davies' season 15 plan, as the returning showrunner has already drawn on his predecessor's efforts since his return.

Doctor Who could fall back on its reliable explanation of Mundy and Belinda being nothing more than just distant relatives.

Alternatively, Doctor Who could fall back on its reliable explanation of Mundy and Belinda being nothing more than just distant relatives. If Davies wanted to avoid another massive storyline like Clara's connection to Eleven, then this would be an easy way to avoid that. However, if this was the case, I doubt a tease like this would have been included in the trailer alongside other huge-looking plots. Only time will tell how Doctor Who season 15 solves this dilemma.