Chinese smartphone maker Xiaomi is losing its head of international and primary English-language spokesperson Hugo Barra after he announced his exit from the company.

Former Android executive joined Xiaomi 3.5 years ago, in what was then a major coup, so his exit naturally raises questions about why he is departing. This year, for the first time, Xiaomi declined to provide annual sales figures and admitted it grew too quick, raising doubts about whether it can continue the impressive growth that gave it a $45 billion valuation two years ago.

Brazil-born Barra said in a Facebook post announcing his departure that his primary motivation is home sickness and that he plans to move back to California:

What I’ve realized is that the last few years of living in such a singular environment have taken a huge toll on my life and started affecting my health. My friends, what I consider to be my home, and my life are back in Silicon Valley, which is also much closer to my family. Seeing how much I’ve left behind these past few years, it is clear to me that the time has come to return.

He added that the company’s global footprint, which was his primary responsibility, is “in a very good place.”

At the time of his arrival, the Xiaomi business was limited to Greater China. Under his leadership, it has expanded across Asia and beyond to reach more than 20 countries, although the U.S. is not on that list. But there have been challenges. Xiaomi has seen its crown as China’s top smartphone maker slip under competition from Huawei and up-and-coming phone makers Oppo and Vivo, so expanding globally became a more important priority in that light. It isn’t yet clear how Xiaomi has done in that respect.

India has been its brightest spot — Barra himself has spent plenty of time in the country — and Xiaomi said that it reached $1 billion in annual revenue in India for the first time in 2016. In a company-wide letter, Xiaomi CEO Lei Jun spoke of his desire to continue to expand Xiaomi’s overseas reach, but it hasn’t provided any additional figures about how it has got on so far. Now, the company is faced with the challenge of replacing Barra — who is well-liked and respected across the industry thanks to his five-year spell with Google-Android — with a figure who can take its global push to the next level.

Xiaomi co-founder Bin Lin, also a former Google executive, said senior vice president Xiang Wang would lead Xiaomi’s international business going forward. Wang, a former head of Qualcomm China, joined Xiaomi in 2015 and previously led its supply chain and intellectual property teams.

Bin also payed tribute to Barra’s tenure with the company.

When Hugo joined us 3.5 years ago, we started an amazing adventure to turn Xiaomi into a global player. We have come a long way since, and I couldn’t thank him enough for contributing so much to Xiaomi’s journey. As much as we would love to have Hugo stay with us in Beijing for a much longer time, we understand his personal challenges and wish him all the best in his future endeavors.

Barra said he will leave Xiaomi in February following Chinese New Year. His immediate plan is to take some time off to rest before “embarking on a new adventure back in Silicon Valley.”