Amit Zavery, VP of Google Cloud and vocal Microsoft critic, announced he is resigning from Google in “one of the toughest” decisions he’s ever made.

Zavery has been in the news a great deal recently, as much for his criticism of Microsoft’s cloud business as for anything else. He has repeatedly accused Microsoft of leveraging its desktop and office suite monopoly to further its cloud ambition, to the detriment of Google and other cloud rivals.

In a LinkedIn post, Zavery said he is leaving Google, but touted the work he helped do to significantly increase the company’s cloud business.

The decision to leave Google is one of the toughest I’ve ever made. Working at Google has truly been a once-in-a-lifetime opportunity and tremendous honor. Over nearly six years, I’ve learned an incredible amount, had so much fun, and witnessed remarkable growth in the business. Helping grow Google Cloud from $7.3B to over $41B in annualized revenue and contributing to the creation of the world’s fourth-largest enterprise software company, has been a career-defining privilege.

Zavery made special mention of Google Cloud CEO Thomas Kurian, with whom Zavery worked with both at Oracle and then Google.

Among the many positives, one stands out above all: the opportunity to learn from my mentor and friend, Thomas Kurian. Over the span of more than 25 years—between Oracle and Google—I’ve had the privilege of reporting to Thomas. I’ve seen many leaders in action, but none quite like him. His consistent ability to understand markets, delve into any subject matter, distill complex information into actionable decisions, and relentlessly pursue positive outcomes with a customer-centric focus has been a masterclass in leadership. The toughest part of leaving Google Cloud is stepping away from the opportunity to work with and learn from Thomas on a daily basis.

Zavery did not reveal his reason for leaving, but he did hint at an upcoming opportunity.

While this goodbye is bittersweet, I’m excited about the new adventures and opportunities ahead. I look forward to staying in touch, collaborating in the future, and continuing to learn from this incredible community. Go Google Cloud!!

It will be interesting to see where Zavery ends up next. In the meantime, however, Microsoft may get a slight reprieve from the criticism coming out of Google Cloud.