Arsene Wenger had earlier admitted to being delighted at being close to signing Pierre-Emerick Aubameyang.
“Yes, it's good news,” Wenger said. “We need people who can give us more offensive power – at the moment we are not efficient enough going forward and I'm convinced he will bring us that.
Dortmund sporting director Michael Zorc couldn’t resist a parting shot at Aubameyang: “Apart from the unpleasant episodes in the past few weeks we would like to remember that Pierre-Emerick Aubameyang at BVB was a real success story."
The 28-year-old has been at Dortmund since 2013 and has scored 141 goals for the club.