Silvercar, Inc., a rental car startup that uses only silver Audi A4 sedans in its fleet, has secured funding from that same German luxury car brand to fund future growth.

Audi AG, a division of the Volkswagen Group, led the $28 million Series C round with Audi’s North American president Scott Keogh joining Silvercar’s board of directors. In partnership with Audi, Silvercar will use the new cash to expand its service to new markets and beyond airports through a new service dubbed Audi Shared Fleet, which will allow businesses to offer cars to employees on their corporate campuses.

“Silvercar represents not just the future of the rental industry, but a vision for the future of mobility,” Keogh said in a statement. “We want to utilize the company’s strengths in technology and innovation to merge connectivity and mobility for today’s consumer.”

Silvercar, launched in 2012 in Austin, Texas, set out to simplify the airport car rental process. Instead of a vast range of car options and grueling paperwork, customers can only rent one model, in one color – a silver Audi A4 – and booking, pickup and payment is simplified through the company’s mobile app and website.

Once a customer has booked a car, they simply scan a QR code on any of the available cars to unlock it and drive off. Billing is handled automatically via the app using an on-file credit card, just like payments on Uber and Lyft’s apps.

The latest investment is the biggest single cash injection Silvercar has received and comes as the company tripled its business in 2015. In the last six months, the company expanded to new markets including Las Vegas, Fort Lauderdale, Chicago and New York City and now operates at 12 Airports across the U.S.

Including the new round, Silvercar has raised $59 million in four rounds from eight investors, including Austin Ventures and Facebook co-founder Eduardo Saverin.

The partnership between Audi and Silvercar is the latest in a number of such accords between traditional automakers and tech-driven startups.

On Monday, Lyft Inc. announced a $500 million investment from General Motors Inc. and rumor has it that Google and Ford Motor Co. are also about to announce a partnership.

Additionally, BMW, Ford and GM have all invested in car-share partnerships in the last year.

Screenshot: SiliconANGLE via Silvercar