Star Trek's William Shatner and Leonard Nimoy were the best of friends on-screen for nearly 30 years – but their relationship in real life was more complicated.

Shatner is opening up about the rift that grew between him and the Spock actor in his new book Leonard: My Fifty-Year Friendship With a Remarkable Man – commissioned after Nimoy's death last year.

"We had some disagreements to begin with, and in the end," he admitted to NBC's Today. "In between was a brotherhood, and I loved it."

While stressing that he and Nimoy were "brothers" in spite of their rift, Shatner acknowledged regretting not making peace while Nimoy was alive.

CBS via Getty Images

"I sought to find out why - couldn't," he recalled. "I thought whatever it was would blow over, he'd tell me what it was.

"I would try to make amends or find some common ground - but he died before that could happen. I miss him."

The duo's friendship dates back to the mid-'60s, when they pioneered science fiction television on the original Star Trek series.

They would later reunite for a series of successful Star Trek movies that lasted from the late-'70s all the way to the mid-'90s.

Nimoy passed away on February 27, 2015 following a long battle with chronic obstructive pulmonary disease (COPD).

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