In December 2017, Boeing's (BA  ) then-CEO Dennis Muilenburg said that the first person who set foot on Mars would get there on a Boeing rocket, beating Elon Musk's SpaceX. But nearly seven years later, NASA is turning to SpaceX to return the astronauts who went to the International Space Station (ISS) aboard Boeing's Starliner spacecraft.

7 Years Ago: "Eventually we're going to go to Mars and I firmly believe the first person that sets foot on Mars will get there on a Boeing rocket," Muilenburg told CNBC host Jim Cramer in December 2017, as reported by Fortune.

Musk responded to the comment on X and said, "Do it." Boeing accepted the challenge, responding to the rival CEO with a short, "Game on!"

The Boeing Company@BoeingReplying to @elonmuskGame on!3:29 PM · Dec 7, 2017

Fast Forward To 2024: On Saturday, NASA announced that it would return the two astronauts who went to space via Boeing's Starliner spacecraft - Sunita Williams and Butch Wilmore - via a SpaceX vehicle in February. The Starliner spacecraft would return to Earth autonomously in early September, the agency said, citing its commitment to safety.

Williams and Wilmore launched into space on June 5 aboard Boeing's Starliner spacecraft. Though the two were supposed to return in about eight days, technical issues identified with the spacecraft while docking delayed the return journey, and now the agency has decided to scrap bringing the astronauts back on the Boeing spacecraft altogether.

Musk Reacts: Musk on Saturday expressed optimism for the future of Boeing despite the setback.

"The new Boeing CEO is spending time in the factories. That is the right thing to do," Musk said. The new Boeing CEO, Kelly Ortberg, took the reins of the company from Dave Calhoun earlier this month.

Had SpaceX not been around, NASA might have turned to Russia to bring the astronauts back home, Musk said in another post. The billionaire also opined that aircraft companies will not dominate the space industry.