Fans of the popular BBC sci-fi programme Doctor Who have been left terrified by the most recent episode of the show featuring shapeshifting aliens.

The show, which started as normal as any episode of Doctor Who can, quickly changed tone and became a little too scary for some fans.

Some took to social media to express how scary and bemusing the episode was when horrifying aliens took the shape of Donna and the Doctor and began chasing the pair.

Doctor Who fans call newest episode 'nightmare fuel'

Fans on X (formally known as Twitter) described the newest episode as "horrifying" with many going as far as to describe it as "nightmare fuel".

One user shared a picture of the 'mirror' version of David Tennant contorted in an unnatural position with the caption "nahhhhhh #DoctorWho."

One user said: "This is weird and creepy and I actually love it" while another added: "Well, that was horrifying."

A fourth fan said: "Oh okay we’ve returned to the ‘absolute nightmare fuel’ variety of Doctor Who. Cool. Cool cool cool cool."

This comes amid Doctor Who's 60th-anniversary special episodes featuring former show stars David Tennant as the Doctor and Catherine Tate as Donna Noble.

The first of these episodes - titled The Star Beast - aired on Saturday, November 24 and featured a guest performance from Miriam Margolyes as unlikely BBC villain Beep the Meep.

The episode saw the Doctor and Donna attempt to stop space super-fugitive Beep The Meep as they attempted to escape Earth (which would have destroyed London in the process).

The next episode is set to air next week (December 9) and is titled The Giggle, featuring How I Met Your Mother star Neil Patrick Harris as The Toymaker.

All episodes of Doctor Who can be found on BBC iPlayer in the show's very own Whoniverse section.