Few would have expected him to still be standing in the dugout when he was named the youngest coach in the history of the Bundesliga back in February 2016, yet here he is: one of the most coveted young strategists in world football today.
Hoffenheim were teetering on the brink of relegation when Nagelsmann was prematurely thrust into a position he was destined to take some four months later. With seven wins from 14 games in charge of a club already written off by the majority of experts, the former Under-19s coach swiftly started to get people to stand up and take note as Hoffenheim somewhat miraculously avoided relegation.
"I think very highly of him, because he has transformed Hoffenheim completely," said Germany coach Joachim Löw, leading Nagelsmann's tributes. "He's very capable, has empathy and a good connection with the players. He has very good prospects."
In spite of his Houdini heroics, very few were giving him much of a chance of taking Hoffenheim further forward than the 15th position they occupied at the end of his brief induction in Bundesliga football.
Watch: Hoffenheim's tactical wizardry
However, in 2016/17 Nagelsmann continued to send jaws dropping and feed humble pie to his ever-reducing number of critics. Hoffenheim were the last club in all of Europe's top five leagues to lose a game, having played the entire first half of the season without being vanquished, while they did not lose a single match at their WIRSOL Rhein-Neckar Arena home. Not even one.
The reward was Hoffenheim's first ever qualification for Europe, with a place in the UEFA Champions League play-off round, and an extension of his contract until 2021, after being named Germany's Coach of the Year for 2016 by the German FA.
"He's a bit different from other coaches, and not just because he's the youngest in Bundesliga history," said Hoffenheim forward Andrej Kramaric. "Julian has everything it takes to become one of the greatest coaches ever. The players are delighted to go into every training session with him, and that's how we approach our games. This is why were are enjoying such a good period."
That good period seems set to last with Nagelsmann "very much looking forward to the challenges coming our way" and keen to pay the club back even more for their faith in him with more of the same: success.
Watch: Hoffenheim's coaching prodigy
Although Hoffenheim came up short in their Champions League play-off with Liverpool, the long-term future of the 2017/18 Europe League participants is glaringly bright - thanks to a mere 30-year-old who has mastered his trade in a matter of 18 months.
Think you know your Hoffenheim? Put your knowledge to the test!