Actor Mark Hamill is expected to reprise his role as Jedi Knight Luke Skywalker in the new Star Wars Episode VII film next year but first he revealed some secrets that most fans do not know about.

"I didn't know that!" said Harrison Ford to co-star Mark Hamill when he realized that Darth Vader was actually Luke's father when he saw it onscreen for the first time during an early screening of Empire Strikes Back.

As Hamill told the story in a Reddit AMA chat yesterday, he shared that he was the third person ever to learn about the greatest secret in Star Wars history.

"[Director] Irvin Kershner brought me aside and said, 'I know this, George [Lucas] knows this, and you'll be the third person who knows. If it goes out we'll know you leaked it,'" the 62-year-old typed speedily online. "I was terrified of being the one to ruin it."

Hamill then discussed how much he knows about the new Star Wars movie.

"I'm worried about Episode VII," he admitted of the upcoming J.J. Abrams-helmed continuation. "They're going after casting sheets! I'm someone who doesn't want to know what I'm getting for my birthday."

Then Hamill also revealed a unique encounter he had with a fan many years ago.

"The strangest [fan encounter] was a cab driver who kept telling me about the anti-Christ and how Luke was blocking Darth Vader's path to taking over the world. He wanted me to help out somehow. I wasn't exactly sure how, but he was very passionate about it," said Hamill in the Reddit AMA.

When asked in the chat what his favorite lightsaber color was, he told an interesting story about another Star Wars alumnus.

"I just worked with Samuel L Jackson and he reminded me he had a purple lightsaber, which nobody had. I thought that was cool that he got his own color. My favorite is green, I'm happy with what I had. You don't need to give me lavender or raw umber or whatever," said Hamill.

Star Wars Episode VII will make its long awaited return to the big screen on December 18 2015.