All the Doctor Who Christmas specials (and New Year specials under Chris Chibnall's reign) hold an interesting place in the show's timeline. Because they're one-off installments, they need to include high-paced action while also maintaining the spirit of the holidays. However, there's often a behind-the-scenes hurdle that needs to be overcome at the same time.

Although Doctor Who's modern era has taken the Doctor through several holiday tropes to varying degrees of success, but the person by his side can often be an unfamiliar face. While this isn't necessarily a bad thing, it does highlight a repetitive streak that must come to an end in December 2025.

"Joy To The World" Is Another Doctor Who Christmas Special Where The Doctor Is Sad About Losing A Companion

The Doctor is often downbeat in Christmas specials due to a friend leaving the TARDIS

Although 2005's "The Christmas Invasion" has Billie Piper's Rose Tyler make the transition between two Doctors, many of the December specials that have followed David Tennant's debut as Ten have had the Time Lord quietly mourning the loss or departure of a previous companion. For example, Ten had just lost Rose to a parallel dimension immediately before the events of 2006's "Runaway Bride." In 2007, "Voyage of the Damned" shows Ten making a comment to Kylie Minogue's Astrid Peth about how it's best that he travels alone, after Martha Jones (Freema Agyeman) chooses to leave the TARDIS.

Although it makes sense that the Doctor wouldn't be in the best of spirits, it starts to get repetitive.

The trend even made the jump to Matt Smith's era as Eleven, when he was quite clearly upset by the loss of Amy Pond (Karen Gillan) and Rory Williams (Arthur Darvill) in 2012's "The Snowmen." Unfortunately, the Doctor Who Christmas specials often fall between seasons, when a previous companion commonly steps away. So, although it makes sense that the Doctor wouldn't be in the best of spirits, it starts to get repetitive. With Millie Gibson's Ruby Sunday staying behind with her family at the end of Doctor Who season 14, "Joy to the World" will also feature a morose Doctor.

Varada Sethu Must Stay Beyond Doctor Who Season 15 To Avoid The Same Trap

Sethu is confirmed to be playing a new character rather than reprising her "Boom" role

Although "Joy to the World" will temporarily install Bridgerton star Nichola Coughlan as Fifteen's sidekick, Varada Sethu's Belinda Chandra is set to take over from Ruby as the Doctor's primary companion when season 15 begins in 2025. It's far too soon to know whether Sethu will remain in her role after the end of next season, but if she does, then she will be able to avoid the Doctor's feeling of loss in 2025's Christmas special - unless Doctor Who has something dark in store for Ruby's confirmed return.