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Ajax secured a deal for the forward in February, but he has now arrived at Amsterdam and begins his five-year contract.
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The base fee is believed to be €15.75m, but could rise to €21.75m or more with bonuses, while Sao Paulo have a 20% sell-on clause.
The transfer is the most expensive in Eredivisie history and he is expected to be the long-term successor to Ziyech, who is now a Chelsea player.
'He will need time like Neres'
"Everyone calls him a wunderkind, but Brazilians are often praised to the sky," Ajax sporting director Marc Overmars told Algemeen Dagblad in February.
"Once he gets here, he will need time, just like David Neres.
"We will be more active in the summer market then we were this winter. I think that when it comes to Antony, we will have a good chance because we can offer talents the best overall package.
"The whole deal will cost around €25m."
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