She resigned from her post last year after leading various parts of Google and its parent company Alphabet for more than two decades.

“Even as I write this, it seems impossible that this is true,” Alphabet CEO Sundar Pichai wrote in a note to employees posted on the company’s website on Friday.

“Her loss is devastating for all of us who know and love her, for the thousands of Googlers she led over the years, and for the millions of people around the world who looked up to her, benefited from her dedication and leadership, and felt the impact of the incredible things she created at Google, YouTube, and beyond.”

Wojcicki was a key figure from the company’s formative days, when she rented her Palo Alto garage to founders Larry Page and Sergey Brin.

In 2016, Wojcicki spoke at Fortunes Most Powerful Women Summit with founder Grace Helbig and Fortunes Jennifer Reingold on the development of media, the creator economy and her vision of YouTube as the future of television.

Read Fortune’s Obituary for Susan Wojcicki here.