The "Doctor Who" Christmas special has sparked a row with the family of actor Nicholas Courtney.
The episode - which marked the end of Peter Capaldi's run as the Time Lord - saw comedian Mark Gatiss appear in the role of Captain Archibald Lethbridge-Stewart, who is a relative of the late actor's recurring character Brigadier Alistair Lethbridge-Stewart.
But the creation of the captain has angered the estate of one of Lethbridge-Stewart's original creators, Mervyn Haisman, and it is currently weighing up whether to take legal action.
Andy Frankham-Allen, creative director of the Haisman Estate, explained to the Daily Mirror newspaper: "Characters are considered creative works and are protected by copyright law.
"As such, we reserve the right to determine what is officially part of our intellectual property.
"If derivative works are created without our permission, then we will determine if/how they fit into our IP. We reserve the right to accept or reject any additions to our intellectual properties."
The character of Brigadier Lethbridge-Stewart made his debut in 1968 and featured in more than 22 storylines on the show.
However, the BBC has denied the suggestion of any wrongdoing.
The broadcaster said: "This claim is without foundation. There has been no breach of copyright."
The row comes shortly after Peter Capaldi revealed that he asked for his final scenes as Doctor Who to be amended at the last minute.
The 59-year-old actor asked the departing show runner Steven Moffat if his final moments could be tweaked because he didn't feel "comfortable" with it.
Peter - who has been replaced as the Doctor by Jodie Whittaker - said: "We're all very concerned about how the Twelfth Doctor leaves us. We're hypersensitive about trying to make it the best we possibly can.
"I had sort of expressed a little discomfort about one of the scenes leading towards the end - and he rewrote it. He rewrote it completely, and quite brilliantly, overnight. Which is fantastic. The downside is I had to learn it overnight!"