Musk was appointed to run DOGE by President Trump when he won the Oval Office, after the duo formed a political alliance ahead of the November election.

Since then, DOGE has been a controversial cost-cutting agency ripping through government departments, including education and USAID.

It is the action taken in USAID that caught the attention of Microsoft co-founder and billionaire philanthropist Bill Gates.

In an interview with the Financial Times earlier this year, Gates said: “The picture of the world’s richest man killing the world’s poorest children is not a pretty one.”

Musk, worth $376 billion per the Bloomberg Billionaires Index, hit back yesterday in an interview with Bloomberg while appearing remotely at the Qatar Economic Forum in Doha.

Musk called Gates a liar, adding: “Who does Bill Gates think he is?”

It was pointed out to Musk that Gates had donated billions to philanthropic causes in some of the poorest parts of the world, including, most recently, a pledge to donate virtually all of his wealth to his foundation.

Gates recently told Fortune the funds, which will total approximately $200 billion, must be spent by 2045 when the foundation will close.

The most recent criticism from Gates, in an interview published earlier this month, came in relation to Musk’s acknowledged mistake about a claim that condoms were being sent to Gaza in the Middle East, with DOGE cancelling the payment via USAID.

It was put to Musk that the contraceptives may instead be bound for the Gaza region of Mozambique to help fight AIDS and HIV infection.

“I’d love for him to go in and meet the children that have now been infected with HIV because he cut that money,” Gates told the FT.

Per Fortune’s own reporting, one charity operating in Gaza, Mozambique did have contracts worth $33m cut by USAID.

In March Trish Karlin, executive vice president for business development and external affairs at the Elizabeth Glaser Pediatric AIDs Foundation, told Fortune the funds were bound to be spent on the “healthcare workforce, support for counseling, testing, blood samples to see how people are progressing in their disease, what other opportunistic infections they may have, psychosocial support training. In some cases logistics.

“We’ve seen stories of drugs are arriving in country but [there’s no] system to then get those medications to the pharmacy. It’s a complex service.”

Musk says he asked for evidence and was met with silence

Speaking to the audience in Doha, Musk said he has gone back over the data and checked whether it could have led to any deaths of children, or indeed the “millions” of casualties Gates has warned of.

“I’d like him to show us any evidence whatsoever that that is true,” Musk said. “It’s false. What we found with USAID cuts—and by the way, they haven’t all been cut—the paths of USAID that were found to be even slightly useful were transferred to the State Department. They’ve not been deleted, they’ve simply been transferred to the State Department.

“But many, many times over with USAID and other organizations, when they said ‘Oh this is going to help children’ or ‘It’s going to help some disease eradication’ or something like that, and then when we asked for any evidence whatsoever, I said: ‘Well please, connect us with this group of children so we can talk to them and understand more about the issue,’ we get nothing.”

Musk continued that philanthropic organizations had declined to present a “show orphan” to illustrate their need for funds, and continued: “What we find is an enormous amount of fraud and graft.

Musk then asked to see which programs have had funding cancelled that could lead to deaths and added: “If in fact this is true, which I doubt it is, then we’ll fix it.”

Representatives for both Musk and Gates were approached by Fortune for comment.