This happened at the 2016 Academy Awards when DiCaprio won the Best Actor award for his role in "The Revenant." In his acceptance speech, he specifically mentioned his fellow nominee, Matt Damon, who was also nominated for his role in "The Martian." DiCaprio said that Damon was "one of the greatest actors of our time" and that he "should have been here holding this award tonight."
This was a very gracious gesture and a testament to DiCaprio's sportsmanship, even in the midst of winning a prestigious award.