Sergiño Dest completed his transfer to FC Barcelona on Thursday.
Ajax will receive more than 21 million euros for the right back, who signs a contract with the club of trainer Ronald Koeman until mid-2025.
Dest's exact transfer fee is 21,230,000 euros.
That amount can increase by five million euros due to bonuses.
The three-time international of the United States, who was still under contract with Ajax until mid-2022, has a departure clause of 400 million euros in his five-year contract with Barcelona.
For some time it looked like Dest would relocate this transfer period at Ajax.
The nineteen-year-old wing defender has also been in the serious interest of Bayern Munich for months, but still opts for Barcelona.
The Spaniards needed a new right back due to the departure of Nélson Semedo to Wolverhampton Wanderers.
Despite the transfer problems, Dest has participated in all Ajax matches in recent weeks.
The former youth player of the team from Amsterdam, who had to tolerate Noussair Mazraoui in the right back position this season, played his 38th and last official match for Ajax against Vitesse (2-1 win) on Saturday.
Agreement with Ajax for transfer of @sergino_dest!
Avatar Author FCBarcelonaMoment of places12: 20 - October 1, 2020
Dest becomes a teammate of Frenkie de Jong
Dest will be the teammate of Frenkie de Jong at Barcelona and is the 21st Dutchman to wear the shirt of the Spanish superpower.
He is also in the top ten of the most expensive departing Ajax players ever.
It is not the first time that Ajax has lost a fixed value during this transfer period.
Hakim Ziyech (Chelsea), Joël Veltman (Brighton & Hove Albion) and Donny van de Beek (Manchester United) left Amsterdam earlier.
Ajax already presented Dest's successor with Sean Klaiber earlier on Thursday.
The 26-year-old right back comes over from FC Utrecht and signed a contract with the team from Amsterdam until mid-2023, with an option for another season.
See also: Overview: All completed summer transfers in the Eredivisie