Who is Outlander's Buck MacKenzie? The time-travelling 'nuckelavee' from the twist ending in episode six?

Episode six of Outlander season seven, 'Where the Waters Meet' has just aired and fans have been left scratching their head after watching the return of an old nemesis in the final moments of the show. 

Since Bree and Roger moved with Jem and Mandy back to the twentieth century and into Lallybroch, the children have been complaining about the presence of a 'nuckelavee'. Bree and Roger weren't really sure if the children were just making up an imaginary friend, but when Roger found rubbish around the property, it seemed to convince him that there was a person trespassing on their land. 

In the final moment of episode six, the mystery surrounding this 'nuckelavee' came to a head as Roger confronted a man dressed in 18th-century clothing outside of their home. Roger looked shocked as he recognised this man from the past, but some fans were confused as they struggled to place who this person was - and why he is significant to the story?

"I’ve just watched the episode with the reveal and I can't for life me put a name to the nuckelavee !!" complained one fan on Twitter. So who is the nuckelavee and what does this mean for Roger and Bree?

*Warning: This article contains spoilers for Outlander season 7 episode 6.*

The nuckelavee who Roger confronted is none other than William Buccleigh 'Buck' Mackenzie, the illegitimate son of Dougal Mackenzie and the time traveller Gellis Duncan, and additionally a distant relative of Roger's.

The last time we saw Buck he was played by Graham McTavish in season five, who of course played Dougal Mackenzie in the earlier seasons of the show. However, some of the confusion about this character may have arisen because the actor portraying Buck is now Diarmaid Murtagh, not Graham McTavish.

Roger and Buck are of course related, but their family ties are rather confusing and their history from the previous seasons is also a distant memory at this point! But don't fret, we can remind you!

In season 5 episode 7, 'The Ballad of Roger Mac' Roger is hanged from a tree after Buck turned him over to the militia and told them that he was a Regulator. Thankfully, Roger was quickly cut down from the tree and he managed to survive because he put his hand between his neck and the rope. Of course, this left a fair bit of bad blood between Buck and Roger - which is why Roger may have felt compelled to punch him at the end of the last episode! 

This was Buck's last appearance in the show so the last time we saw him was with his wife Morag and their son Jeremiah, firmly in 18th century North Carolina.

Why Buck is now in the 20th century we don't know, his mother was a time traveller so perhaps he must have inherited Geillis's ability to pass through the stones and has either come to the future on purpose or by accident. We suspect more will be revealed in the next episode, as Bree and Roger will have to figure out what to do with this unwelcome guest!