Chris Cox, one of Facebook’s early engineers and a close friend of Mark Zuckerberg, said he decided to leave the company, CNBC reported. 

“It is with great sadness I share with you that after thirteen years, I’ve decided to leave the company,” he said.

Zuckerberg also announced the resignation of Chris Daniels, who is responsible for the WhatsApp messenger owned by Facebook.

“Chris is one of the clearest and most principled business thinkers I’ve met and the diversity of challenges he has helped us navigate is impressive,” Zuckerberg wrote.

In a statement Thursday, the company blamed a “server configuration change that triggered a cascading series of issues” for the outages. The company said its services were coming back online.