There were, of course, a few high-profile cameos: singer and songwriter Judy Collins called, and sang a verse of “Amazing Grace” at Rehm’s request. Isabel Wilkerson, author of “The Warmth of Other Suns,” also phoned in: “Oh Diane, you’re such a national treasure.” Sen. Cory Booker, D-N.J., thanked Rehm for her “incredible service” to the country, and legendary actress Julie Andrews and her daughter gushed their love and gratitude, calling Rehm “a beacon of light in our lives.”

But many of the most touching sentiments were expressed by Rehm’s everyday listeners, those who had followed her work for decades — the “back-of-the-car” babies, as she calls them, who first heard her voice on their parents’ car radios.

“I really wanted to thank you for your numerous shows through the years that have brought us closer to the day when equal rights and religious liberty for all Americans truly will become a reality,” said one self-identified gay man. His voice broke as he repeated: “I just wanted to thank you.”

Rachel from Grand Rapids, Mich. thanked Rehm for being a role model to girls everywhere. “I just wanted to say, on behalf of all women, we just appreciate everything you’ve done on radio for us.”

Rehm’s career on the air began in 1979 when she became the host of “Kaleidoscope,” a weekday arts program aimed at homemakers; five years later, she re-launched it as “The Diane Rehm Show,” with the aim to tackle a broader and more ambitious range of topics. Only a few years later, she was diagnosed with spasmodic dysphonia, a disorder that causes spasms of the vocal cords and is responsible for her distinctive, strained speech. At first, the condition threatened to doom her career; instead, the petite woman with the fragile voice went on to become a Peabody Award-winning powerhouse of radio, drawing nearly three million listeners every week.

Last year, she announced that it was time to step away from the microphone. She’d promised her boss that she would leave the show when she turned 80, she said. In an interview with The Washington Post’s Karen Heller, Rehm said that she looked forward to having more freedom to devote herself to causes that mattered to her. Her husband of 54 years, John Rehm, died a slow death in 2014 after deciding that he didn’t want to suffer from Parkinson’s disease any longer, and refused food, water and medication. Since then, Rehm has become a vocal advocate in the right-to-die movement — and her active involvement in a controversial issue drew admonishment from NPR’s leadership. After she leaves her show, that conflict will no longer stand in her way, she said.

“It’s time for me to retire, especially on the issue of right-to-die, to be able to speak out and to speak freely,” Rehm told Heller in January.

She will be succeeded by Joshua Johnson, whose show “1A” will air on member stations across the country.

Rehm has emphasized that she isn’t really leaving, not entirely — she plans to host a new podcast, “On My Mind,” which she says will likely launch in late January.

But as the minutes ticked toward noon on Friday, it felt like the end of an era nonetheless.

“So now comes the time to say goodbye, having been in daily touch with you pretty much for the last 37 years, and having it come to an end is difficult for me,” she said. “Physically, I know I’m ready. Emotionally, I only think I’m ready, because I know it’s going to be a hard adjustment: changing habits, shifting thoughts from a daily deadline, missing being with wonderful colleagues. But there comes an end to all things.”

She thanked her “fabulous” audience: “You are kind, you are thoughtful, you are courteous,” she said. “You exemplify civil conversation, and I’ve been proud to be your host.”

Then Rehm shared some sad personal news: Her beloved little dog, Maxie — a familiar character to Rehm’s longtime listeners, and the subject of a book she wrote in 2010 — had passed away Saturday.

“He died in my arms,” she said. “He was 13 and a half years old, and my apartment feels so empty without him.”

But in the final moments of her last show, she struck a more hopeful tone. It was on to new things, she said, and she hoped her listeners would follow her to her new podcast.

“Really, it’s not goodbye, it’s farewell,” she said as she signed off, just before the familiar theme music began to swell. “For now, I send all of you my love, and my prayerful hope for a Merry Christmas, and a peaceful new year.”