Viktor Gyokeres says he decided to sign for Arsenal after the Gunners thrashed his Sporting side 5-1 in the Champions League last season.
The 27-year-old Sweden striker has joined Arsenal in a deal worth up to 73m euros (£64m) on a five-year contract.
The move was held up because of negotiations between the clubs over additional payments, with the final agreement consisting of a 63m euro initial fee plus 10m euros in add-ons.
Gyokeres was in the Sporting side dismantled by Mikel Arteta's team in the group stage of Europe's top competition in November.
"I just felt it was the right club for me," said Gyokeres. "What I heard from Mikel and [sporting director] Andrea Berta and just what I've seen in the past years, how they've been playing football.
"When I played against Arsenal last season, I could really feel it was a very strong team and very difficult to play against.
"That made me choose Arsenal, and of course all the history the club has and the massive fan base."
The move takes Arsenal's summer spending up to about £204m, following the arrivals of Martin Zubimendi, Kepa Arrizabalaga, Christian Norgaard, Noni Madueke and Cristhian Mosquera.