WASHINGTON, United States (AFP) — US President Donald Trump said Thursday he was “very disappointed” by Elon Musk’s criticism of his policy mega-bill, adding he didn’t know if his friendship with his billionaire former advisor would survive.

In an extraordinary rant in the Oval Office as visiting German Chancellor Friedrich Merz sat mutely beside him, Trump unloaded on SpaceX and Tesla boss Musk in his first comments on the issue.

“Look, Elon and I had a great relationship. I don’t know if we will anymore. I was surprised,” Trump told reporters in the Oval Office after former advisor Musk slammed the bill as an “abomination”.

“I’m very disappointed, because Elon knew the inner workings of this bill better than almost anybody sitting here… All of a sudden, he had a problem,” Trump added.

The 78-year-old president then delved into the deteriorating relationship with Musk.

His comments come less than a week since he held a grand Oval Office farewell for Musk as he wrapped up his time leading the cost-cutting Department of Government Efficiency (DOGE).

Musk stunned reporters at the time by turning up with a black eye that he said was caused by his son.

“You saw a man who was very happy when he stood behind the Oval desk, and even with the black eye. I said, you want a little makeup? We’ll get you a little makeup,” Trump said.

“But he said, ‘No, I don’t think so,’ which is interesting and very nice. He wants to be who he is.”

Trump said he could understand why Musk was upset with some steps he had taken, including withdrawing a nominee to lead the NASA space agency whom the tech tycoon had backed.

The US president’s “big, beautiful bill” on tax and spending — the centrepiece of his domestic agenda — could define his second term and make or break Republican prospects in the 2026 midterm elections.

Musk however called it a “disgusting abomination” on Tuesday. A day later, the magnate called for Republicans to “kill the bill,” and for an alternative plan that “doesn’t massively grow the deficit.”