The current Doctor Who production schedule has episodes shooting over a year before they air. This necessitates an appropriately timey-wimey relationship between casting announcements and on-screen appearances. Ncuti Gatwa was announced as the Doctor over 18 months ahead of his on-screen debut.

At this rate, we may very well have a 16th Doctor announced before we get through the first season of the 15th Doctor. 😬

https://variety.com/2024/tv/global/doctor-who-millie-gibson-varada-sethu-1235880343/

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