Larry Page, the billionaire co-founder of Google, is secretly backing a pair of startups that are working on flying cars, according to a report.

Since 2010, Page has poured more than $100 million into Zee.Aero, a company that lately has been testing two flying-car prototypes at an airport hangar in Hollister, Calif., Bloomberg said Thursday, citing sources.

Since last year, Page also has been funding another flying-car startup called Kitty Hawk — and has cast it as a rival to Zee.Aero as he stages a top-secret race to develop a new class of vehicles that can soar above traffic jams and sidestep the hassles of the airport, Bloomberg said.

“Page has drawn a line separating his two flying-car teams,” the report said. “It’s common for the Zee.Aero engineers to speculate over lunch about what their Kitty Hawk counterparts are up to.”

Zee.Aero, which has tapped top talent from firms like SpaceX, NASA and Boeing, is headquartered in a 30,000-square-foot building right next to Google’s home offices in Mountain View, Calif., according to the article.

Inside, Page initially set up a “man cave” on the second floor, outfitted with a bedroom, bathroom, expensive paintings, a “treadmill-like climbing wall,” and one of SpaceX’s first rocket engines — a gift from Page’s pal Elon Musk, according to the report.

Page’s upstairs bunker earned him the nickname “GUS” from Zee.Aero employees — short for “guy upstairs,” the report said.

Zee.Aero has since expanded to 150 employees and moved Page out of the second floor.

The company also runs a manufacturing facility on a NASA research campus at the edge of Mountain View, according to the article.

Meanwhile, Kitty Hawk, which employs about a dozen engineers and has its headquarters about half a mile away from Zee.Aero, is working on “something that resembles a giant version of a quadcopter drone,” according to Bloomberg.

Kitty Hawk’s president, according to 2015 business filings, was Sebastian Thrun, th­e creator of Google’s self-driving car program and the founder of its research division Google X, whose “moonshot” projects have included artificial intelligence and robotics.

“Page once vowed to a colleague that if his involvement in the sector ever became public, he might pull support from the companies,” the report said.