Elon Musk's tumultuous US$44 billion ($70b) bid to buy Twitter is on the verge of collapse — after the Tesla CEO sent a letter to Twitter's board saying he is terminating the acquisition. 

Twitter did not immediately respond to a message for comment. It is not entirely clear whether Twitter's board will accept the US$1 billion breakup fee or if there will be a court battle over the deal. 

The possible unravelling of the deal is just the latest twist in a saga between the world's richest man and one of the most influential social media platforms. Much of the drama has played out on Twitter, with Musk — who has more than 95 million followers — lamenting that the company was failing to live up to its potential as a platform for free speech.