It was the end of 2016 and she was running Sam’s Club, Walmart’s warehouse club division. Starbucks’ chief executive Howard Schultz was visiting the retailing giant’s Bentonville headquarters for a panel discussion with Walmart (WMT) CEO Doug McMillon.

But at the last minute, McMillon had to cancel so Brewer stepped in. She and Schultz “were probably on stage for about 90 minutes,” she tells Fortune. “We just hit it off.”

Brewer soon made her own trip out to Seattle with her team to visit Starbucks’ flagship roastery for a tour and discussion about the digital revolution of retail. The 10-minute drop-in she was supposed to have with Schultz lasted more than an hour. Schultz asked if she’d ever considered joining the board. “And I said, ‘No, not really. I’m not interested in another board seat, but thank you very much,’” Brewer recalls. “And then by the time I got to the airport, I was thinking what did I just do?”

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At the time of the visit, Brewer was thinking about the next phase of her career. She’d been with Walmart for a decade and had just taken Sam’s Club through a digital revamp. “I actually felt like my work was done there and I wanted to repeat that somewhere else where I had a little more influence and control,” she says. She ended up stepping down from Sam’s Club in February, a month after it was announced she would join the Starbucks board.

Starbucks CEO Kevin Johnson, who took on the top job from Schultz in April, didn’t start thinking about Brewer for the COO role until about two months ago. She’d impressed him as a director with what he describes as her insightful questions, ability to connect with people, and her operational prowess—plus he’d heard Brewer was looking for something new. He asked for advice from some other board members who encouraged him to reach out. So he picked up the phone.

“I said, ‘Roz, this might sound crazy to you, but if you’d be interested, I’d really love to have this conversation,” Johnson says. She flew out to Seattle the next weekend. Brewer, who will become the first woman and first African-American to hold such a senior post at Starbucks, will remain on the board even after she begins the job in October.

Johnson and Brewer have followed similar paths at Starbucks. Johnson, a tech industry veteran, also started as a board member before joining the company as COO and president in 2015.

Johnson says that the Starbucks board isn’t intentionally designed to be a feeder pool for talent but because it’s a “culture first company and values matter, that means getting to know people well—whether that means the leadership team or the board or their candidates from outside the company.”

Brewer says that as Starbucks becomes increasingly focused on technology, one of her jobs will be to make sure it’s operationally flawless. “When you begin to add digital components on top of your business, you have to make sure the basics are there,” she says. “The partners have to accept technology first before they can transfer it to the customer.”

That’s something the company will need as it smooths out its mobile order and pay system, which had a challenged launch. “It’s in my wheelhouse,” she says. “I had to do that at Sam’s and I’ll repeat that again here at Starbucks.” She says she’ll also focus on inventory management as Starbucks continues to grow its food business.

Brewer says her first point of the action will be better understanding the coffee business. She has two grande iced green teas (unsweetened, extra ice) every day and goes for a flat white when she really needs the caffeine. As part of her immersion as a board member, she spent some time behind the bar making lattes. “I will tell you that I’m really empathetic for the work they have to do,” she says of the company’s employees. She wants to simplify the jobs of store employees—the people she says who work the hardest at the company, who Brewer has a real affinity for.

“That immersion was a real eye-opener for me,” she says, “and really set me on the right course to think about this company in a different way.”