The first official teaser trailer for Star Wars: The Last Jedi has triggered a series of fan theories, including one about "piece of Darth Vader's lightsaber".

In The Force Awakens, Kylo Ren emerged as a new antagonist for the series, but the mystery behind his frantic search for his uncle Luke Skywalker remained largely unexplored.

A new theory by dedicated fan website Making Star Wars suggests that the latest film will revolve around Kylo's efforts to get hold a crystal worn by Luke.

The website claims that Mark Hamill's character wears a mysterious necklace in Star Wars 8, which has a deep connection with Darth Vader and will fit into the narrative of the upcoming film.

According to MSW, the "red crystal or gem" at the bottom of the necklace, is a "piece of Darth Vader's lightsaber". The website speculates that the gem was the power source of the late Sith Lord's weapon and Kylo probably knows its secret.

Hence he is trying to find Luke to get the precious stone and "stabilise his own lightsaber".

Here is what Jason Ward of MSW wrote about the mysterious necklace:"If Luke Skywalker has the last Darth Vader Kyber crystal, someone like Kylo Ren would really want it. I don't know why Luke Skywalker doesn't just destroy it. But he would clearly see that someone as into symbolism as Kylo Ren would be even more of a monster if he possessed it. If it is a story element, will Kylo get it back and stabilise his saber with the power source of his Grandfather's lightsaber?"

Kyber crystals have long been part of the Star Wars lore, featuring in last year's Rogue One as well, and it seems now an new stone will play a major role in the eighth film in the space action saga.

The Last Jedi stars Daisy Ridley, John Boyega and Adam Driver, and is directed by Rian Johnson. It will open in theatres on 15 December 2017.