Dortmund confirmed the deal on Thursday (via the Bundesliga), with Guerreiro signing a four-year contract with his new club:
The German side beat Premier League pair Arsenal and Liverpool to sign Guerreiro, and Dortmund sporting director Michael Zorc said he was delighted the defender opted to move to Signal Iduna Park, per DW Sports: "Guerreiro is a technically skilled player who feels at home in several positions. We are very happy that he chose Borussia Dortmund."
The Portugal international—currently playing at Euro 2016—blossomed into one of the best full-backs in Ligue 1 with his former employers and is ready to make the step up to a more illustrious club.
German football writer Stefan Buczko previously reported that Dortmund would pay around €12 million (£9.5 million) for Guerreiro, something of a bargain for a player of his quality:
Here is what Dortmund supporters can expect from their new man:
Having been snapped up by Lorient in 2013 from Caen, the 22-year-old Guerreiro has gone from strength to strength.
He cemented his position in their first team with some very capable performances, showcasing attacking endeavour and energy on the left flank. They were displays that didn’t take long to catch the attention of his national-team selectors, and Guerreiro made his debut for Portugal in November 2014. He’s already scored two goals.
As Portuguese football writer Jan Hagen noted, the left-back has been impressive in his appearances at the elite level:
They’re standards he will be keen to keep up at his new home. Dortmund may have to be patient with Guerreiro as he seeks to acclimatise to a new playing style and a new culture off the field. But there’ll be a pressure on the ex-Lorient man to offer a similar kind of vibrant edge when scurrying down the left wing.
There are areas where Guerreiro needs to make adjustments. Defensively, he can be caught a little flat-footed at times, and those frailties will be ruthlessly exposed in the Bundesliga. Additionally, he can sometimes be rash in the tackle and worked over by physical wide players.
Still, there’s a lot of talent to work with for Dortmund manager Thomas Tuchel and a lot of time for the left-back to undergo these developments in his game. For those reasons, and for all the positive attributes he already possesses, this is an exciting capture.