The Union officially announced Friday that Brenden Aaronson, their 19-year-old star playmaker, will leave the team at the end of this season to join Austria’s Red Bull Salzburg.

Multiple sources with knowledge of the deal told The Inquirer that Salzburg will pay a $6 million transfer fee for the Medford native, plus up to $3 million in performance bonuses. Those sources said the bonuses shouldn’t be too hard achieve.

There’s also a sell-on fee, which means if Salzburg sells Aaronson to another club in the future, the Union will get a cut of the proceeds. The fee ranges from 10-20% depending on the nature of such a deal.

Aaronson will be eligible to play for Salzburg starting on Jan. 1. His contract there will run until the summer of 2025.

It’s a historic moment for the Union on many levels, starting with Aaronson being the first product of the team’s Wayne-based youth academy to be sold abroad. The fee is the largest ever for a Union player. The previous record was set seven years ago when Michael Farfan was sold to Mexico’s Cruz Azul for just over $300,000.

The fee is also the largest ever for an American product of a MLS club academy, topping the $5 million that England’s Chelsea paid the New York Red Bulls for Matt Miazga in January 2016. The only bigger fee for an academy product in league history was Canadian phenom Alphonso Davies' $13.5 million move from the Vancouver Whitecaps to Germany’s Bayern Munich in August 2018.

Aaronson started his journey to pro soccer with a Union youth team as a 10-year-old, then joined the team’s full-time high school in Wayne after his freshman year at Shawnee. He began playing for the Union’s minor-league USL team as an amateur in 2017, then moved up to MLS at the start of 2019. In his two years in the big leagues, he has been one of MLS’ top young players, with a highlight reel mix of speed, dribbling skill, passing vision, and scoring punch.

“His dynamism and his presence on the field are extraordinary for a 19-year-old,” Red Bull Salzburg sporting director Christoph Freund said. “Despite his young age, he already has an excellent feeling for making the right decisions on the pitch."

The deal is not just validation for Aaronson but for Union sporting director Ernst Tanner, who came here from Salzburg two years ago to accelerate the academy’s progress. His task was to not just develop players but make them good enough to be attractive to European suitors — and make the deals to sell them on. This is his first success, and it’s a big one.

It helps that Tanner has personal connections to Aaronson’s new club, having worked as Salzburg’s youth academy director from 2012-18. He also had a hand in Salzburg’s development of players who now rank among Europe’s brightest stars, such as Sadio Mané and Naby Keïta of reigning English Premier League champions Liverpool.

“It’s my job,” Tanner said. “It’s good to know that we can do it here as well, and in addition I think it’s a great opportunity for [Aaronson], and it’s a great honor for our club. That’s for sure.”

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Since Tanner left, Salzburg has continued to be one of Europe’s preeminent talent factories. The club has dominated Austria’s domestic league and become a regular presence in the star-studded UEFA Champions League, and its current manager is Princeton alum Jesse Marsch — a former teammate of Union manager Jim Curtin in MLS.

“We’ve watched Brenden Aaronson for some time now, and I think he’s gotten better and better with each game," Marsch said. “He’s very aggressive, he runs all day, he’s clever on the ball, he does all the things that we like as a player. ... I know that he’ll do great here.”

Last season, Marsch helped turn Norwegian striker Erling Haaland into one of the world’s hottest prospects. Haaland exploded on to the global stage with eight goals in the Champions League, prompting Borussia Dortmund to buy him for $24 million midway through the season. Another Salzburg phenom , Japanese winger Takuma Minamimo, earned a $9.5 million transfer to Liverpool at the same time.

“They have such a big pedigree [of] developing players even more, and making them into stars,” Aaronson said. “Seeing them [be interested], I really was like, ‘Wow, this is awesome.'”

If Aaronson succeeds at Salzburg, he will also vault up the U.S. national team’s depth chart. His versatility as a playmaker could make him an ideal candidate to back up superstars Christian Pulisic and Giovanni Reyna, and he could have a shot at the 2022 World Cup team. Nor is it far-fetched to imagine him playing in the 2026 World Cup in the United States — including at Lincoln Financial Field, should Philadelphia be picked as a host city.

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The current generation of local youth soccer players hang posters of Hershey’s Pulisic, Delran’s Carli Lloyd and Coatesville’s Zack Steffen in their bedrooms. Aaronson could join them in the coming years.

“Brenden will be among [MLS'] role models, because he has played and developed in MLS,” Tanner said. “MLS is definitely a good league for young players, not only to transition from youth to the first team but hopefully the transition over to Europe in the future as well. That’s the standard we need to develop, and Brenden will be an excellent example.”

Aaronson has long dreamed of making that transition overseas. But it’s one thing to be drawn to the continent’s bright lights, and another to actually get playing time there. That mattered to him when multiple European suitors came calling, including high-profile teams in Germany.

“I wanted to go to a club that I could develop more [at] and get stronger as a player, and where I’m going to be challenged, and I think that Salzburg was the perfect place for me,” he said. “I wanted to go somewhere and have more of a chance of playing than go to some big team in Europe. … I wouldn’t want to make that jump quite yet because I want to go somewhere where I think I can start and play more.”

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In addition to elevating Aaronson, the deal is validation for the Union’s multimillion dollar investment in its youth academy. Not only has it now delivered a major return, it has done so with a player who’s a genuine creator. Though Aaronson doesn’t wear the famous No. 10 jersey, he plays its traditional role of midfield playmaker — one of soccer’s most sacred positions.

“To see a kid come through that maybe doesn’t just play as an outside back or a hard-working midfielder, to play as a No. 10 in Europe is a real proof of concept,” said Curtin, who has known Aaronson for nearly a decade. “There’s no better kid, and there’s no better player to be the first one [from the Union] to go to Europe.”

Aaronson will be missed when he leaves, for sure. But as teammates such as Anthony Fontana and Mark McKenzie have shown, the Union’s academy has turned into a conveyor belt of professional-quality talent.

“I couldn’t be more happy about our academy than now,” Tanner said. “And the people in the stadium … when they announce the names, the people cheer now when they hear an academy boy. And I don’t think that has always been the case in Philadelphia.”

» READ MORE: Brenden Aaronson played four positions in the Union’s win over FC Cincinnati

Tanner is right about that. The Union have been overlooked by many Philadelphia fans throughout their 10-year history, and haven’t been a big deal in MLS. But Aaronson’s talent and the big transfer fee will bring unprecedented attention. As with college basketball and football recruiting hype, fans and scouts will want to know who’s next.

“We are very proud of Brenden and what he has accomplished in such a short amount of time,” Union majority owner Jay Sugarman said. “Brenden’s success will inspire everyone involved in developing our young talent and will be just one of many success stories we expect to see out of our academy in the coming years.”

The next crop of academy prospects is already on the way, and one of them is Aaronson’s 17-year-old brother, Paxten. He won’t just be following Brenden’s footsteps into MLS: he’s a midfield playmaker too, and the early word is he could be even better.