NEW YORK — It’s the next step in the biggest celebrity story of the year: the long-awaited debut of Caitlyn Jenner’s series charting her new life as a woman.

Fittingly, “I Am Cait” (premiering at 8 p.m. Sunday on E!) opens with the former Bruce Jenner, her ample tresses in huge rollers, at home getting hair-and-makeup treatment as she beholds a giant blowup of her bombshell Vanity Fair cover after her April interview with Diane Sawyer.

Yes, Jenner’s transition from Bruce to Caitlyn has been a highly orchestrated spectacle, with “I Am Cait” the latest phase of the campaign. And, typical of celeb-reality shows, there isn’t a scene in this first of eight episodes that doesn’t seem stage-managed to push the starry uber-narrative along.

Even so, there is something more substantial going on here. A gratifying measure of authenticity manages to bypass the celebrity trappings.

Jenner’s mother and two sisters help. Delivered to Jenner’s seaside California compound for their first encounter with her as a woman, they seem refreshingly like regular folks who are genuinely focused on a family member they love and support, never mind all the lights and cameras there to capture every moment.

“It’s going to be so difficult for me to think of you as ‘she,’ and say ‘Caitlyn’ when I want to speak with you,” her mother says. “It’s going to take some getting used to, but I want to do what you want.”

At the hour’s end, Jenner heads to San Diego to meet with the mother of Kyler Prescott, a transgender teen who took his own life in May.

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