Spencer Wilding, who hails from Rhyl, was the guest of honour at a special screening of Rogue One.
He had to muster all powers of the force to keep his Vader role secret until the film's release.
"It's a hell of a secret to keep," said Wilding, who was cast as the body actor for the role.
"But when you're a professional actor - when you sign that black and white sheet of paper saying you cannot say a word... I'm true to my word and I didn't say anything."
Speaking to BBC Radio Wales' Good Morning Wales programme, the 44-year-old said it proved a tricky task after rumours of the role leaked a year ago.
"I've been having hundreds of people every day for a year asking me if I'm Vader," he said.
"If I had a pound for everyone who asked I'd be buying myself a new Death Star - and it'd be gold plated."
The 6ft 7in (2m) tall actor already has a string of Hollywood appearances to his name, including Guardians of the Galaxy, Green Lantern, three Harry Potter films and the TV blockbuster Game of Thrones.
He said the Vader role came from a regular casting call, first with a self-filmed tape, then a recall to Pinewood Studios.
"It's very, very secretive. We didn't even know exactly what the character was and what film it was until we got there," he said.
"I opened up the curtain when I went in the dressing room and there he was - Vader.
"Anybody out there who got into that costume and got an audition to be Darth Vader alone is very exciting, so to pull the character off as well, it's like 'What!'
"I'm always pinching myself - I am definitely awake - it is not a dream, it is just another dream come true."
While the actor has the body role, just like his predecessor in the original Star Wars films David Prowse, the voice of Lord Vader is actor James Earl Jones.
That did not stop Wilding trying out the voice during filming.
"I'm not James Earl Jones - nowhere near him - but you know I got close to him I think, which helped the other actors - you know, you've got Vader in front of you."

In a statement in the official Granma newspaper, the government described the project as "a serious error".
"The symbols of the Revolution are and will always be sacred," it read.
The colognes - Ernesto and Hugo - were unveiled on Thursday by a state laboratory in the capital, Havana.
Labiofam said Ernesto, the cologne named after the Argentine-born revolutionary who helped Fidel Castro take over in Cuba in 1959, would be a woodsy and refreshing citric scent with notes of talcum powder.
Hugo, named after the late Venezuelan president, would offer a softer, fruitier fragrance with hints of mango and papaya.
"They will be very attractive colognes, but the names also mean a lot to us," said Isabel Gonzalez, vice-president for research and development for Labiofam during the launch.
But the project was mocked in the social networks and criticised by supporters of the Cuban Revolution, who considered it disrespectful.
Labiofam had been in the process of developing stylised bottles and labels for the products before putting them on sale in Cuba and overseas.
"We didn't want to create propaganda, but rather pay homage to them and help their names endure," said Cuban biochemist Mario Valdes, who led the scent design team, on Thursday.
The company said it had obtained the agreement of the families of Che Guevara and Hugo Chavez to use their names in the colognes. But that has now been denied by the Cuban government.
"The details of this irresponsible action were discussed in detail on Friday with the company's director and the employees who presented the products, which were still being developed," read the statement of the Executive Committee of the Ministers' Council, headed by Cuban President Raul Castro.
"The appropriate measures will be taken to deal with this serious error.
"Such initiatives will never be accepted either by our people or by the Revolutionary Government."
Darth Vader and Imperial Stormtroopers have invaded a Denbighshire seaside town to welcome the actor who plays the infamous villain.
[NEXT_CONCEPT]
The Cuban government has said it will take disciplinary action against a state pharmaceutical company that created perfumes named Ernesto Che Guevara and Hugo Chavez.