Once a key member of President Donald Trump's inner circle, Elon Musk's relationship with the president has deteriorated into a bitter public feud.

An intense public feud erupted on Thursday between President Donald Trump and his one-time ally, billionaire Elon Musk, with an argument about Trump’s massive tax and domestic policy bill raging across social media and in the Oval Office.

Donald Trump and Elon Musk exchanged back-and-forth insults online after a disagreement over the president's spending bill. Here's a complete timeline of Donald Trump and Elon Musk's friendship, including why they are now feuding.