The news was released earlier through the official website (see photo below), then removed because their performance as concert series opener was supposed to be a guessing contest on the website.
A little later a special “Meet and Greet” contest was added here:
To purchase tickets for the event, click here. (As Big Bang is performing on the main stage in zone 4, make sure you purchase the Zone 4 tickets)
Photo via: sayseungri and chrome_hurts (Twitter)
N.B: Technically the announcement of Big Bang’s participation at the event was part of another “Guess Who” contest that is open for fans to guess and vote on until July 3rd, but someone accidentally already posted the news on the official media portion of the site before removing it. Both the “Meet and Greet” and the “Guess Who” are still open and available on the Singapore Grand Prix website.
Via: Big Bang Updates