Kyle Larson waves to fans as he leaves the track after the Indianapolis 500 on Sunday. Larson was trying to make it to to the NASCAR Cup Series race in Concord, North Carolina in time to race, but once he arrived the race was called off because of rain. Darron Cummings/Associated Press

CONCORD, N.C. — Kyle Larson spent a year preparing to run the double.

Instead, he got to run only a single, leaving the NASCAR star beyond disappointed.

Larson’s quest was to complete – if not win – the Indianapolis 500 and Coca-Cola 600 on Sunday, joining Tony Stewart as the only drivers to do all 1,100 laps in a single day. But then rain intervened not once but twice, and a rookie mistake at the Indy 500 cost him a chance to contend in the one race he ran.

“What I thought could be one of the best days of my life quickly turned into one of the most disappointing ones I’ve ever experienced,” Larson said on social media Monday, roughly 12 hours after storms in Charlotte prevented him from climbing into his No. 5 car to finish the NASCAR race.

When rain pushed back the start of the Indy 500 by four hours, Larson’s team made the decision to stay and run the race. He made a mistake going through gears at one point, costing him 10 spots, and his pit-road speeding penalty ended any chance of winning. He wound up finishing 18th.

The 31-year-old Larson tried to make the best of a bad situation, taking two helicopters and a private jet to reach Concord with the Cup Series race just past the halfway point. The crowd cheered his arrival on pit lane, and Larson donned his race helmet and readied to get into the No. 5 Chevrolet.

That’s when the race went under caution, and a steady downpour forced a red flag. Two hours later, NASCAR declared race leader Christopher Bell the winner with 151 laps remaining, saying there was no way to dry the track and resume racing until after 1 a.m. because of the humidity.

Larson never took a lap at Charlotte.

“So much time, money and effort went into this experience and it just kills me to have it all end the way it did,” Larson said. “I feel like I let so many people down. We knew all along weather could throw a wrench into things but seeing it come to reality is a horrible feeling.”

Larson said he was disappointed for car owner Rick Hendrick, apologized to his race team in Indianapolis for his mistakes and expressed frustration for the documentary crew that had followed his eight-month journey but was robbed of a great story by storms in two different states.

Larson’s focus now returns to NASCAR and attempting to win his second Cup Series championship.

NASCAR rules stipulate a driver can’t participate in the postseason without running every race. That means Hendrick Motorsports will need to file a waiver on behalf of Larson, asking for special permission for the 2021 season champion to race in the playoffs.

That hasn’t been done yet, but given the attention Larson brought to the sport over the last few weeks, it is almost unfathomable that the governing body would not grant one.

Last year, NASCAR gave Chase Elliott the opportunity to make the playoffs after he was suspended for intentionally wrecking Denny Hamlin in the Coca-Cola 600.

Despite rain that washed out much of Indy 500 practice, Larson said attempting “The Double” was one of the best experiences of his life – right up until Sunday. And afterward, Larson expressed his desire to try it again; Hendrick Motorsports and Arrow McLaren have a two-year deal to field a car.

“I can’t describe how appreciative I am of everyone’s support of me to live out a dream,” Larson said. “I hope it’s not the last opportunity I have to try ‘The Double’ but if it is I guess it was memorable.”