Amazon and Blue Origin founder Jeff Bezos is reportedly pouring millions into a mysterious anti-aging research startup in Silicon Valley — efforts that are already earning him derision from space competitor and fellow billionaire Elon Musk.

The startup, called Altos Labs, is looking into ways to reverse aging in human cells. That type of work has shown some promise, but is still in its very early stages.

“And if it doesn’t work, he’s gonna sue death!” Musk chided in a characteristically scathing tweet on Tuesday, a jab at Bezos’ highly litigious tendencies.

The beef between the two richest men in the world has been stewing for months now — but as far as we can tell, it’s the first time Musk has ridiculed Bezos for actions unrelated to space exploration.

The most recent zinger comes as Bezos’ efforts to curry favor with NASA and be signed on as a second Human Landing Systems (HLS) contractor in addition to SpaceX are arguably becoming increasingly desperate.

Both space companies — in addition to Alabama-based Dynetics — were competing for funding from the space agency to develop a lunar lander capable of taking US astronauts to the Moon.

But SpaceX emerged as the sole winner, to Bezos’ great dismay. Last month, Blue Origin decided to sue NASA over its decision, which led to NASA temporarily pausing the entire program — and Musk mercilessly raking his rival over the coals.

“Turns out Besos [sic] retired in order to pursue a full-time job filing lawsuits against SpaceX,” Musk tweeted late last month, referring to Amazon filing a lawsuit to slow down SpaceX’s plans to expand its Starlink constellation.

Musk even suggested that SpaceX “zap [Bezos] on the head with our space lasers” last week.

“He should consider spending some money on actual lunar lander hardware, instead of shady lobbyists,” Musk suggested in a separate tweet, after news broke that Blue Origin hired former Amazon consultants with ties to a controversial Pentagon contract.

And now, it appears, Musk and Bezos’ bickering has breached beyond the topic of space exploration. Musk is out for blood, and not afraid of hitting below the belt.

Where the squabble will end up taking us — and how it will continue affecting NASA’s efforts to return astronauts to the Moon — remains to be seen.