Owls boss Carlos Carvalhal is expecting big things of Adam Reach after capturing the winger before last night's 11pm transfer deadline.
It is understood Wednesday have forked out a club-record transfer fee to bring the 23-year-old to Hillsborough. Reach has joined in an initial £5m deal which could rise with add ons by a further £2m.
Wednesday beat off strong competition from several Championship clubs to land Reach, who spent much of last season on loan at Preston North End.
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Carvalhal said: "Adam is a player that we have followed since last season and we believe in him a lot.
“He is a young player and a player with a bright future in our opinion. We believe in his abilities and also that in the future he can get better and better.”
Reach, a graduate of Boro's youth system, has penned a five-year contract. He will wear shirt number nine and could make his Owls debut in their home encounter with Wigan Athletic after the two-week international break.
Outlining the attributes Reach will bring to his team, Carvalhal said: "Adam is very competitive, a hard worker and a player that will understand the values of Sheffield Wednesday.
“He knows a lot about Sheffield Wednesday, the fans, the club, the team and even though we know a lot of teams were trying, we are very happy because he chose to come with us.”