According to Malika Andrews of ESPN.com, Doncic—who tallied 18 points, 11 rebounds and 10 assists in the loss—became the second-youngest player in league history to accomplish the feat at 19 years and 327 days old.
Philadelphia 76ers guard Markelle Fultz was 19 years and 317 days old when he tallied a triple-double in April 2018, also against the Bucks.
While Doncic made history, he was upset that he shot 6-of-17 from the field in the loss.
"I played bad for sure," Doncic said, per Andrews. "I got my triple-double, but I would prefer the win, and I didn't play good at all."
Doncic has been a revelation for the Mavericks in his rookie season. He entered Monday averaging 20.0 points, 6.7 rebounds and 5.1 assists per game while serving as one of the team's primary ball-handlers and its go-to scorer.
He has demonstrated the ability to read the defense and make the right play, whether it is attacking the lane and unleashing a soft floater or forcing defenders to collapse and finding an open teammate. His style of play is conducive to racking up triple-doubles, and Monday's showing was likely the first of many to come.
Doncic is also in position to potentially start in the All-Star Game. The NBA's most recent release of fan voting results has him second among Western Conference frontcourt players, trailing only LeBron James. Fan votes constitute 50 percent of the voting total, while players and the media make up the other 50 percent.
Doncic's Mavericks are five games behind the Los Angeles Clippers for the No. 8 seed in the Western Conference, but he is providing hope for a bright future in Dallas nevertheless.