Eustaquio made 157 appearances during his four and a half years at Porto.
He scored 11 goals and provided 12 assists for the Dragons while helping the club to a string of domestic trophies.
Born in Canada to Portuguese parents, Eustaquio moved to Portugal as a child.
He played for Torrense, Leixoes and Chaves and, after a brief stint in Mexico at Cruz Azul, returned to Portugal with Pacos de Ferreria, where his form secured a move to Porto.
Eustaquio had a spell on loan at Los Angeles FC earlier this year in order to get game time before the World Cup, but concedes it has not been easy to say goodbye to Porto, a club he has grown to “call home”.
“I had amazing experiences there,” he adds.
“Basically I entered [Porto] as a kid and I leave as a man.
“But just like life, we have to move on and I’m glad that I have that experience in my backpack to keep going.”
Though he had to brush up on Swansea before agreeing to this week’s move, Eustaquio was aware of the club’s Premier League history.