Armie Hammer as Clyde Tolson in “J. Edgar.” In real life, Hoover may have kept a file on Hammer’s great-grandfather Armand Hammer because of his ties to the Soviet Union. (Keith Bernstein)

Armie Hammer had zero hesi­ta­tion about signing up to play Clyde Tolson, the former FBI associate director, purported lover of history’s most famous G-man and a key character in the new biopic about that G-man, “J. Edgar.”

“I actually had more creative reservations about playing a prince than I did about playing Clyde,” Hammer, 25, says via telephone, referring to his role as Prince Albert Alcott, the Prince Charming character in director Tarsem Singh’s upcoming “Mirror, Mirror.” Playing Tolson was “something I could do to stretch me and make me grow as a person.”

It says something about Hammer’s ambition — as well as how quickly his star has risen since his dual turn as the Winklevoss twins in last year’s “The Social Network” — that he is able to go from playing the love of J. Edgar Hoover’s life in a Clint Eastwood film, which opened Wednesday, to the charmer who makes Snow White swoon in Singh’s fairy tale, due in March. And it might speak to a certain fearlessness, necessary when one portrays the lover of a controversial figure whose sexual orientation still sparks debate.

Hammer — who hired a professional researcher to dig up any and all scraps about Tolson, from photos to his FBI job application — seems to have little doubt about the relationship between Hoover (played by Leonardo DiCaprio), who died in 1972, and Tolson, who inherited Hoover’s estate and lived there until his death in 1975.

“If you had a co-worker who was a guy and you two showed up to work together every morning, you went to lunch together, you went to dinner together, then you drove home together where you lived together, and then you showed up for work the next morning together, I mean, people would make assumptions, naturally,” Hammer says.

“We did take some artistic liberties,” he adds, “but I think more than anything else, we just sort of connected the dots.”

“J. Edgar’s” dots suggest there was a deep romantic love between the two men but one that Hoover was too repressed to fully express. Tolson, on the other hand, comes across as fully comfortable with his homosexuality, albeit not officially “out.”

That’s a portrayal to which some object. In a recent USA Today story, Cartha “Deke” DeLoach, a former aide to Hoover, said he met with DiCaprio and emphasized that he “never saw any evidence” of a gay relationship.

Hammer says he also spoke with DeLoach. “He just had nothing but the most respectful and professional things to say, almost as if J. Edgar’s reach extended past his grave and he could still ax him,” the actor says wryly.

(For the record, Hammer’s great-grandfather, oil tycoon Armand Hammer, was scrutinized by the FBI head because of his ties to the Soviet Union, according to a book written by Edward Jay Epstein.)

Regardless of how the Hoover/Tolson relationship is perceived, the film undoubtedly will provide another boost to Hammer’s rising career, which next affords him the opportunity to play the Lone Ranger opposite Johnny Depp’s Tonto in Disney’s new take on the adventure serial. Hammer is approaching the “Hi-yo, Silver!” hero the same way he delved into Tolson: doing research and running lines with his wife, journalist and occasional actress Elizabeth Chambers.

“She knows exactly when I’m lying, so if I’m acting with her, she’ll just go: ‘Uh-uh. I don’t know why, but it seems like you’re lying.’ It’s like: ‘Oh, okay. Then I’ll do this and this and this differently.’

“It’s the most terrifying thing in the world,” Hammer adds, “which is why I’ve just resigned to never lie to her.”