CHARLOTTE, N.C. (AP) - In an announcement that has rocked the world of racing, Dale Earnhardt Jr. says he's retiring at the end of the NASCAR season because he wants to be able to go out on his "own terms."

He missed much of the 2016 season with concussion-like symptoms, and he acknowledged today that the time off played a role in his decision. He's become an advocate for research of sports-related brain injuries.

Earnhardt, a two-time Daytona 500 winner, just got married and says he wants to start a family.

He says he informed Hendrick Motorsports owner Rick Hendrick on March 29 of his plans to retire. Earnhardt said that "without a shadow of a doubt," the toughest part of his decision was informing Hendrick.

Earnhardt says he is committed to participating in two Xfinity Series races in 2018 and that "even after this season, you have not seen the last of me on the racetrack." 

Fellow drivers are offering tributes to Dale Earnhardt Jr. after he announced his plans to retire.

Tony Stewart tweeted that he's proud of his "great friend" for "everything he's done for this sport." Jeff Gordon, in a statement issued through Fox Sports, says Earnhardt "had a huge impact" on NASCAR.

The news was the latest blow to the stock car series, which lost two other popular drivers in Gordon and Stewart to retirement the past two years.