Andre-Villas Boas has made Gylfi Sigurdsson his first signing as Tottenham head coach.
The former Chelsea boss was only appointed as Harry Redknapp's successor Tuesday, but has moved quickly to bring the Hoffenheim midfielder to White Hart Lane.
The move secures Sigurdsson's return to the Barclays Premier League, where he impressed so much during the second half of last season on loan at Swansea.
The 22-year-old Icelander netted seven times in 19 appearances for the Welsh side and picked up March's Player of the Month award.
Sigurdsson had looked to turn his successful loan spell into a permanent move after Swansea settled on a record-breaking £6.8million fee with Hoffenheim.
The Swans also announced that personal terms had been agreed, but manager Brendan Rodgers' move to Liverpool saw the move falter.
Sigurdsson had been linked with a move to the Reds to rejoin his former manager, but Spurs have swooped to compete the signing of the in-demand midfielder.