Doctor Who includes another nod to the Doctor's family – what does it mean?

Doctor Who showrunner Russell T Davies previously touched on this, saying: "We saw at Christmas, there is obviously a mystery to Ruby's birth family. She was a foundling left at a church. It is a fairy tale-like story, but it keeps following her.

"That story is not finished. Who is her mother? How can they possibly find out what went on? The way the Doctor ties into this is fascinating. This emotional man I've been talking about opens up about his family in a way that he's never done before."

"He left his family behind in 1963 and practically never mentioned it again. That's a man who doesn't know his family, and that is fascinating.

"So as his mind is focusing on that, Ruby's mind is focusing on her family. Those two stories come together in possibly the greatest finale ever committed to film, except we don't actually use film anymore! But it really is an astonishing climax."

Last week's opening double-bill, Space Babies and The Devil's Chord, saw the beginnings of the Doctor (Ncuti Gatwa) opening up to Ruby (Millie Gibson) about their own family, revealing not only that they were adopted but also that they were a grandparent, with the fate of the Doctor's granddaughter Susan left ambiguous.

"The Time Lords were murdered," the Doctor revealed. "Genocide rolled across time and space like a great big cellular explosion – maybe it killed her, too."

This wasn't a one-off – latest episode Boom sees another reference to the Doctor's family, as they use their status as a parent to form a bond with an AI recreation of a slain soldier. (Only in Doctor Who!)

The story, written by former Doctor Who showrunner Steven Moffat, saw the Anglican marine John Francis Vater (played by Joe Anderson) executed by military tech – but it transpires that something of the real Vater survives within his post-mortem holographic avatar, which allows the Doctor to compel Vater's 'soul' to aid him in a battle against the Villengard automated ambulance unit (the face of which is none other than Susan Twist's).

Drawing on Vater's bond with his daughter Splice (Caoilinn Springall), the Doctor urges the hologram to fight back against the ambulance, which is about to provoke a devastating explosion. "Dad to dad, you never let them down, right? Ever. To the end.

"Dad to dad, dust to dust, am I right?"

Doctor Who fans were already speculating that last week's reference to Susan could mean the character is set to reappear on the show – or even that she has some connection to Ruby and her as-yet-unrevealed birth mother – and this latest reference to the Doctor as a father is sure to only stoke those flames...

Read more:

• Doctor Who confirms next Susan Twist role and new cast for 73 Yards
• Doctor Who' Steven Moffat sparks speculation with season 15 finale hint

Speaking exclusively to RadioTimes.com, Carole Ann Ford – who played Susan on the show from 1963 to 1964 – didn't rule out a return for her character.

"Bonnie [Langford]'s character, Mel, was last seen on a far away planet hitching a lift with Tony Selby's loveable rogue Glitz, and then suddenly turned up in 21st century London working for UNIT!" she said, adding that "absolutely anything and everything is possible" in Doctor Who.

Doctor Who continues on Saturday 25th May on BBC iPlayer and BBC One. Previous seasons are available to stream on BBC iPlayer.

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