Tesla’s stock fell by a fell 21 per cent on Tuesday (Sep 8) — the most ever — on news that the pioneering electric car maker was passed over for inclusion in the S&P 500 and an announcement of partnership between competitors Nikola Corp and General Motors.

While Tesla lost about $80 billion of its market value, its CEO Elon Musk’s own net worth plunged $16.3 billion on Tuesday, the largest single-day wipe-out in the history of the Bloomberg Billionaires Index.

S&P Dow Jones Indices, which manages the S&P 500, was widely expected to include Tesla in the prestigious index after it posted its fourth consecutive profitable quarter in July, clearing a major hurdle for its potential inclusion in the benchmark stock index. The expectation of inclusion had in part had driven the frenzied buying of the stock in last few weeks. But in a surprise move, S&P Dow Jones Indices decided to add online craft seller Etsy Inc , semiconductor equipment maker Teradyne Inc and pharmaceutical technology company Catalent Inc to the S&P 500 instead.

The announcement by General Motors that it is picking up a 11% stake in the Arizona-based electric and hydrogen vehicle maker Nikola Corp also contributed to Tesla losing steam in the market.

Phoenix-based Nikola specializes in building zero-emission semi trucks using battery or hydrogen fuel cell technology, but it recently introduced its Badger pickup truck for consumers.

Under the deal, GM will also become the exclusive supplier of fuel-cell technology for Nikola's upcoming Class 7 and 8 semi trucks