Grocery delivery app Instacart, which saw a surge in sales amid the pandemic, announced Thursday that Facebook executive Fidji Simo will serve as its new chief executive. Apoorva Mehta, the company's co-founder and CEO, will become chairman of the board in August amid plans for Instacart to soon go public.

"To be honest, the idea of someone else running the company had never even crossed my mind, but I’ve been blown away by her capabilities as a leader," Mehta told CNBC Thursday.

In March, the San Francisco-based company saw its valuation grow to $39 billion after a new round of funding.

It's been a steady rise for the 35-year-old Simo, who grew up in the seaside town of Sete, France, to a family of fishermen.

She had been at Facebook for over a decade and has overseen the social media giant's “big blue app” since 2019. She had the important role of heading the News Feed, Stories, Groups, Video, Marketplace, Gaming, News, Dating and Ads.

“Fidji is an incredible leader,” Simo’s mentor, Facebook's chief operating officer Sheryl Sandberg, told Marie Claire in a profile of Simo in August 2019. “From the moment we met eight years ago, I could see she’s one of those rare leaders who both see the big picture and go deep into the details to get the work done.”

Simo told CNBC that she sees parallels at Instacart with what she’s done at Facebook and hopes to build Instacart into an “incredible consumer app.”

“We saw the emergence of a lot of new companies built on top of Facebook ads,” she said. “And I’m seeing the same thing happening within Instacart’s business, where not only existing food companies are reaching new customers, but I see new food companies having the potential to be created.”

Mehta told CNBC that his takeaway after spending "hundreds of hours" speaking with Simo and that they both share the same vision for Instacart.

Simo interviewed with Instacart’s board after Mehta reached out to her with a cold email. Instacart announced three of its newest board of directors earlier this year.

Simo told CNBC that she and Facebook CEO Mark Zuckerberg spent several weeks mulling her exit.

“Well, you know, it wasn’t as you can imagine, it wasn’t a one-time conversation,” she said. “It was over the course of several weeks. And, you know, the thing I deeply, deeply appreciate about Mark is that he’s been a supporter from day one, and really wanted to make sure that he understood my motivation and what I wanted to do with my life and what I was looking for. He’s been incredibly supportive throughout the process. Obviously sad that we couldn’t find something that aligned at Facebook, but also incredibly supportive of me taking on this role, which I’m always grateful for.”

Simo officially takes over on Aug. 2.