Ewan McGregor has admitted he was left terrified when he filmed scenes with 'Star Wars' villain Darth Vader for the first time

During an appearance on 'The Tonight Show Starring Jimmy Fallon', Ewan

explained: "It was frightening to see him again though. I hadn't acted with Darth Vader.

"And I've been acting a long time. I think I've done a lot of stuff. But the first take with Darth Vader scared the s*** out of me."

Hayden Christensen has also returned to the 'Star Wars' universe after previously portraying Anakin Skywalker's journey to becoming Darth Vader in the three prequel movies.

In 'Obi-Wan Kenobi', Hayden gets to step back into the famous black suit and Ewan said it was chilling to finally see the actor in full costume.

He told Jimmy: "They went, 'Action!' And I'm walking down and I hear something, I turn around and f*** Darth Vader is coming at me. I swear to god, I just about s*** my pants, really."

Jimmy added: "When you're a kid, that is probably one of the scariest villains you'll see."

Ewan said: "That's it, I think ... I was like seven years old again. It was really, it was really genuine fear. I've made horror films and stuff. They're not frightening, but that was."

Obi-Wan was played by Alec Guinness in the original 'Star Wars' trilogy, with Ewan taking over to play his younger self in the prequels.

The actor admitted he initially struggled to get back into character for the new TV series and ended up having to watch lots of Alec's old movies in a bid to perfect his accent.

He said: "I just had to go back and like watch lots of Alec Guinness movies and watch all the original films. I got back into it. It was good, it was really good fun."