By Hilary Whiteman , CNN Hong Kong Written by

Chinese artist and rights activist Ai Weiwei could soon be on the move again.

On Wednesday, the avid Instagrammer posted a photo of himself holding a Chinese passport to his 110,000 followers with the words, "Today, I got my passport."

Chinese authorities revoked Ai's travel rights four years ago, seizing his passport and declining requests to allow him to leave the country.

In November 2013, Ai pledged to leave a bouquet of fresh flowers on a bike outside his studio at No. 258 Caochangdi in Beijing every day until he regained the right to free travel.

Wednesday marked 600 days since he made that pledge, which he has documented on Instagram every day since for almost two years.

He posted the most recent one earlier on Wednesday, with the words, "Today is 600th day!"

Accused of tax evasion

In April 2011, Ai was on his way to Hong Kong when he was taken into custody at Beijing's International Airport and detained for 81 days amid a government crackdown on political activists. He was later accused by authorities of evading taxes and intentionally destroying accounting documents.

He was released on one year's probation in June 2011, but the government retained his passport.

Ai is best known for designing Beijing's iconic "Birds Nest" Olympic stadium. He later said he regretted working on it because instead of becoming a place for all, the venue served to benefit only the elite.

The Royal Academy of Arts in London was quick to confirm that Ai would be traveling to the United Kingdom in September for a major exhibition of his work dating from 1993.

"This is wonderful news for Ai Weiwei, his family and for artists worldwide. We are delighted to announce that he will be joining us as we finalize the installation of his exhibition at the Royal Academy of Arts, London," said Artistic Director Tim Marlow.

Ai is also reported to be planning to return to Germany, which last year hosted his biggest ever solo show without him. The piece of political comment, which filled 18 rooms at the Martin-Gropius-Bau museum in Berlin, featured a replica white cell where authorities held him during his time in detention.

Ai has been a vocal critic of the Chinese government, and his frustration with the system has been evident in his work. He was particularly critical of the government's response to the 2008 Sichuan earthquake, which killed at least 87,000 people.

A number of his works reference the tragedy, and the exhibition in London in September is expected to include 90 tons of twisted metal retrieved from the quake debris.

China has not yet commented publicly on why Ai's passport was returned.