Latrobe defeated odds-on favourite Saxon Warrior as brothers Joseph and Donnacha O’Brien secured an Irish Derby victory at the Curragh.
The 14-1 shot, ridden by younger brother Donnacha, held off the challenge of Rostropovich and Saxon Warrior.
Trainer Aidan O’Brien was chasing a record 13th Irish Derby win but was denied by his sons.
Joseph, 25, became the youngest trainer to win the Melbourne Cup last year.
Saxon Warrior, ridden by Ryan Moore, was much fancied, even after finishing fourth in the Derby at Epsom earlier this month.
The three-year-old had to settle for third, though. despite a strong finish.
Rastropovich set the early pace and managed to hold off Saxon Warrior as Latrobe took the victory by half-a-length.
Joseph O’Brien won the Irish Derby twice as a jockey in 2012 and 2014 before stepping down from riding to focus on a career as a trainer in 2016.
His father Aidan first won the race as a trainer in 1997.
BBC horse racing correspondent Cornelius Lysaght
The rapid and ongoing rise up the training ranks of Joseph O’Brien barely two years after he switched from race-riding is pretty extraordinary, and he is reaching summits that his father was nowhere near achieving so early in his own career in the 1990s.
That’s a Classic now on top of a Melbourne Cup and some prestigious prizes over jumps, and he’s also winning plenty of ‘ordinary’ races too.
And Donnacha should not be forgotten in all this: that’s a third British or Irish Classic of the year, and rather gives a lie to his own suggestion that he only gets big-race opportunities because of who he is.
That’s not luck, it’s talent.