Lady Gaga replaces Keith Urban at the Indianapolis 500

Lady Gaga stepped in for Keith Urban as a special guest at the Indianapolis 500 race in Indiana on Sunday (29May16) after he injured his back.

The former American Idol judge was supposed to ride in a two-seat IndyCar pace car alongside racing legend Mario Andretti on the Indianapolis Motor Speedway on Sunday, but Gaga suited up instead.

"I have yet to meet her, personally," Andretti told USAToday.com prior to the ride. "She decided to do it, and all of a sudden here we are."

"She's going to distract me quite a bit, actually," he jokingly added. "I hope I can just look ahead while I'm driving."

Gaga celebrated her speedy new gig with fans on social media ahead of the event, sharing a photo of herself standing on a podium with Andretti and his relatives, including grandson Marco Andretti, who was racing in Sunday's historic event.

"Gentlemen start your engines!," she declared on Instagram. "I'm one of the family today".

The pop superstar also posted pictures of herself modelling her blue and white race uniform, greeting Andretti with a hug, holding hands with the veteran driver as they made their way to the vehicle, and making the peace sign as she settled in to the back seat of the car.

Andretti later took to Twitter to mark the occasion at the 100th Indy 500, writing, "I brought @ladygaga back safely to pit lane. Thanks @IRE2seater pit crew and @Honda for your support. Historic Indy!"

Keith, who was not scheduled to perform, has yet to reveal the extent of his injuries, but he took to Twitter earlier in the day to alert fans to his absence.

"Hugely disappointed I can't be in that pace car with Mario Andretti today to celebrate Indy's 100th," he wrote before the race. "But Nic and I are watching at home and cheering on Marco and the whole Andretti family !!!!"

Unfortunately, the star support did little to help Marco secure pole position - he finished 13th, as 24-year-old Alexander Rossi became the first rookie to win the Indianapolis 500 since Helio Castroneves in 2001.