William Shatner opens up about losing his co-star and good friend Leonard Nimoy in a new book, Leonard, subtitled My Fifty Year Friendship With A Remarkable Man,”; and he tells ET Canada about the bond they shared. “A brother I’d never had is the way he and I referred to each other,”; says Shatner.

Meanwhile, In a new interview, the Star Trek star speaks candidly about dealing with agony of wife Nerine Kidd’s accidental alcohol-related death in 1999, and how Nimoy helped him through the pain.

The 84-year-old tells SiriusXM’s Tell Me Everything that no one can understand what an addict goes through.

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“I don’t understand the agony. I am empathetic to the agony. I am in agony myself, not about drinking … but whatever my agonies are,”; Shatner tells host John Fugelsang.

Nimoy, who had struggles with addictions himself, was a helpful friend who was there for Shatner as he tried to cope with his wife’s death.

“[Nimoy] helped me try to understand, Yes, agony belongs to all of us. Agony is party of the soul,”; Shatner explains. “Somebody who hasn’t felt agony hasn’t lived. Hasn’t participated in what life is. But there is a special agony for somebody who wants to give up the addiction and can’t. The shame that they must feel. The self-degradation.”;

RELATED: William Shatner’s Touching Tribute To His Late Friend Leonard Nimoy

Shatner found his wife unconscious at the bottom of their pool, with authorities concluding her addiction to alcohol contributed to the accidental drowning.