Barcelona have completed a deal to sign Borussia Dortmund forward Ousmane Dembele for an initial £96.8m, potentially rising to £135.5m.
The 20-year-old France international signed a five-year contract at the Nou Camp alongside the club's president Josep Maria Bartomeu on Monday.
The deal is the second most expensive of all time, eclipsed only by Neymar's recent £200m move to Paris St-Germain.
Barca said Dembele's contract has a release clause of 400m euros (£369.6m).
Dembele said: "I'm very happy to be here. It has always been my dream to be at Barcelona and now I'm here I'm very happy.
"It is the best club in the world with the best players in the world."
Dortmund said they rejected Barca's approach because their offer "did not correspond to the extraordinary footballing and additional value of the player and the present economic situation of the European transfer market".
With regard to the agreed fee, Dortmund said in a statement the payment of add-ons "was agreed up to a maximum total amount of approximately 40% of the fixed transfer fee".
Barca have failed with three bids for Liverpool midfielder Philippe Coutinho, the most recent of which was £114m.
Officially, the £75m signing of Luis Suarez from Liverpool in 2014 was their most expensive previous purchase.
However, Bartomeu has said in the past that "the overall cost of the operation" to sign Neymar from Brazilian club Santos in 2013 was "over 100m euros (£92m)", despite the transfer fee having been disclosed as £48.6m.
Dembele exploits attract Barca's attention
He joined Dortmund from French side Rennes on a five-year deal in May 2016, having been voted Ligue 1 young player of the year for the 2015-16 season, when he scored 12 goals and made five assists.
Dembele made his senior France debut in 2016, his only goal in seven caps to date coming in a 3-2 friendly victory over England in June.
He was left out of the France squad for September's World Cup qualifiers against the Netherlands and Luxembourg, with manager Didier Deschamps explaining on Thursday: "Ousmane hasn't trained for a fortnight and he's waiting to see if the transfer will go ahead or won't go ahead."
The second biggest transfer ever
2017 - Neymar £200m (Barcelona to Paris St-Germain)
2017 - Ousmane Dembele £135.5m (Dortmund to Barcelona)
2016 - Paul Pogba £89m (Juventus to Manchester United)
2013 - Gareth Bale £85m (Tottenham Hotspur to Real Madrid)
2009 - Cristiano Ronaldo £80m (Manchester United to Real Madrid)
John Bennett, BBC World Service
The transfer fee is astonishing but former team-mates and former coaches will tell you Ousmane Dembele has the potential to be a Ballon d'Or winner.
They mention his extraordinary acceleration on the ball, they rave about how two-footed he is (his right foot is supposed to be stronger than his left, but it's very close) and they talk about his extraordinary skills, touch and close control.
His former manager at Rennes, Rolland Courbis, actually claims Dembele could have joined Barcelona last summer but turned them down. He says they offered more money than Borussia Dortmund but the French youngster chose to go to Germany.
His change of heart now may have a lot to do with Neymar's departure offering more guaranteed game time in a World Cup year. Filling the Brazilian's boots will come with a lot of pressure but Dembele has the quality to make that spot his own.
Find all the latest football transfers on our dedicated page.