"It's a little unfortunate they did that thing with Tupac as we've been trying to make Freddie appear on the stage for quite a while, " he said.

BBC: Freddie Mercury

The event should prove to be a lively one given that it will be the first time that all eight candidates will appear on stage together post Labor Day, when the campaign for the Republican nomination really starts to heat up.

FORBES: GOP Candidates Must Win One For The Gipper

The discussions appear to be at a preliminary stage, and it remains unclear when the authorities will make a decision on or release details about the matter, the people said.

WSJ: China May Give Foreign Pension Funds New Investment Opportunities

There was confusion over what time Bieber was due on stage, with The O2 saying on Tuesday the 19-year-old was scheduled to appear at 21:30, following performances from three support acts, including Carly Rae Jepsen and Cody Simpson.

BBC: Justin Bieber apologises for O2 gig delay