Brunt said the most stirring moment came in October, when Kelly was hosting her show from the oceanside in Dana Point, Calif., where she was attending Fortune magazine’s Most Powerful Women Summit. Unexpectedly, an enormous crowd began to gather. “It was one of those moments when you see how big it has become,” Brunt said.

What happened inside the conference, which was a gathering of the most powerful women in business, was no less extraordinary. Sheryl Sandberg, the chief operating officer of Facebook (FB), who wrote Lean In, was to interview Kelly on the main stage. Sandberg introduced Kelly with a clip from a celebrated Megyn moment from 2013, in which she challenged the conservative commentator Erick Erickson for saying that the national increase in female breadwinners ran counter to the biologically determined order. “Who died and made you scientist in chief?” Kelly asked him.

The conference hall erupted in cheers, and Sandberg herself, who worked in the Clinton administration before her hiring at Facebook, audibly whooped. “I saw that on TV,” she told the crowd, “and I just cold-called her and said ‘I love you, you are awesome.’ ”

I’ve come to know hundreds of successful women since Fortune launched Most Powerful Women in 1998, and it strikes me that Megyn Kelly is a certain type: She’s one of those powerful women who sneak up on you.

I remember the April day last year when Sandberg called me and said, “I know who I want to interview this year at your women’s Summit.” Who? (I expected her to say Hillary Clinton or some other boldface name.) “Megyn Kelly,” she answered. I was silent.

“Do you know who Megyn is?” Sandberg asked. I took a stab and said, “She’s a TV news person.” Sandberg laughed and told me that after seeing Kelly on air, she cold-called her and went on her show and became a fan, whatever their political differences.

I’m embarrassed to tell you that I sternly told Sandberg that I doubt Kelly would be interesting enough for a main-stage Summit interview. Well, as soon as I called my colleagues—one living in Megyn Kelly heartland (South Carolina) and another, Fortune Washington editor Nina Easton, who regularly appears on Fox News—I was shaken out of my Anderson Cooper-centric New York bubble and told: “Welcome to the real world, Pattie.”

And I was one of the hundreds of women wowed last fall when Sandberg interviewed Kelly on stage. Kelly, 44, talked about how she quit a cushy job at a big corporate law firm to try TV journalism at a sliver of her old pay. Like Sandberg, who left a safe and lucrative job at Google (GOOG) to be No.2 to 23-year-old Mark Zuckerberg when Facebook was hardly a clear winner, Kelly took a heck of a career risk. I have no doubt that Sandberg “loves” Kelly in part because Kelly leaned in hard—and every night on The Kelly File, she leans in more by bucking convention.

The on-stage Sandberg-Kelly conversation turned out to be one of the MPW Summit’s highest-rated sessions, not only because these two successful women sync. They made us think about our own power and how to define it. There is positional power, the kind that most people embrace: They do the job they’re supposed to do, not much more, and play it safe. The other type of power is personal power: You do the job you’re supposed to do, and you add to it by defining success your own way. You lean in. And if you lean well, your power doesn’t leave you when your job goes away.

Personal power is harder to achieve (and trickier to recognize), but it is also easier to preserve. And more valuable than positional power can ever be. Kelly and Sandberg have personal power in spades. Enjoy their conversation at the Fortune MPW Summit. You get good career advice here, too.