Finally, a happy ending to a fraught Triple Crown.

Arcangelo thundered down the stretch of the Belmont Stakes to win the 155th running of the Belmont Stakes by a length and a half and made a little history: His trainer, Jena Antonucci, became the first female trainer to win a Triple Crown race, a series that spans more than a century.

The colt held off a late run by Forte and gave his jockey, Javier Castellano, his first Belmont victory. Castellano, a Hall of Famer, won his first Kentucky Derby five weeks ago aboard Mage. Arcangelo is a 3-year-old ridgeling who cost owner Jon Ebbert of Blue Rose Farm $35,000 as a yearling.

It was welcome news to a battered old sport that is under intense scrutiny after 12 horses died at Churchill Downs — two on the undercard of the Derby — and made the public question whether horse racing’s social license should be renewed.

The sport, too, was rocked by the news that Forte, the Derby favorite until he was declared unsound by Kentucky veterinarians and scratched on the morning of the race, had flunked a drug test last September after winning the Hopeful Stakes.

It was one of six failed tests by horses trained by the Hall of Fame trainer Todd Pletcher in the last 11 months.