Iconic Taiwanese boy band F4 (Flower 4) took to the stage over the weekend for their "F Forever City of Stars" concert in the Chinese city of Shanghai, but the reunion sparked controversy as member Ken Chu was noticeably absent from the line-up.

Instead, Ashin from Mayday, a Taiwanese rockband, joined the reunited "F3" members for the concert in Shanghai which is due to conclude on Monday (December 22).

In footage provided by Taiwan-based recording company B’in Music, F4 members Vanness Wu, Jerry Yan and Vic Chou were seen performing on stage with Ashin, as the audience sang along.

Chu's absence has fuelled speculation online, with some suggesting he had revealed details of the upcoming reunion before it could be officially announced by the band itself or the record company managing the band. Chu has denied breaching any agreements that prohibited an unofficial announcement. 

The boyband famously formed in 2001 after the members acted in the Taiwanese idol drama Meteor Garden that same year, but their members went their separate ways in 2009.

-Josh D. Arslan/Reuters