Borussia Dortmund said they were hugely disappointed by the transfer of Mario Goetze, one of the jewels of their youth academy, to arch-rivals Bayern Munich after the season but said they would overcome the midfielder's surprise departure.
The 20-year-old Goetze, who joined Dortmund as an eight-year-old, is regarded as one of the country's most talented young players, has already won two Bundesliga titles and played 22 times for Germany, having also represented them at various age levels.
Losing one of their leading players to Bayern is a bitter pill for Dortmund to swallow and comes as an unwanted distraction on the eve of their Champions League semi-final first leg at home to Spanish giants Real Madrid.
"I think there could have been a worse time to announce this - four hours before the game," said a relaxed-looking Dortmund coach Juergen Klopp.
"I can say time does not heal all wounds but it helps the healing process. The reason we are all disappointed is because he is a great player and we would like to keep him."
Goetze used a release clause to opt out of his contract.
"Mario Goetze and his agent informed Borussia Dortmund a few days ago that the player would like to trigger his release clause and move to Bayern Munich on July 1," the club said on their website (www.bvd.de) on Tuesday.
Recently crowned Bundesliga champions Bayern confirmed the move in a "media explanation", adding that they had intended to announce the signing after Dortmund had played on Wednesday.
"We confirm that Mario Goetze will play for Bayern from July 1," they said, adding that they would match Dortmund's buyout clause.
German media said Bayern would be paying around 37 million euros ($48.21 million) for Goetze which, if confirmed, would be the most ever spent on a German player.
The move means that the technically gifted attacking midfielder, who can also play on the wing, could face his future club in the Champions League final at Wembley on May 25.
Bayern face Barcelona in the other semi-final, with the first leg in Munich later on Tuesday.
Dortmund, second in the Bundesliga, immediately appealed to their fans not to turn against Goetze as they chase Champions League glory.
"Together with coach Juergen Klopp, sporting director Michael Zorc asks all Borussia Dortmund fans to unconditionally support Mario Goetze in the last games of the season, especially in the Champions League semi-final against Real Madrid, just as they would any other Dortmund professional," the statement said.
Despite boasting average home attendances of some 80,000 and recent back-to-back league titles, Dortmund have struggled to hang on to their top players.
Playmaker Nuri Sahin left after helping Dortmund to win the 2011 Bundesliga crown and the Turk has since returned to the club on loan after unhappy stints at Real Madrid and Liverpool.
Shinji Kagawa, who went from a little-known Japanese second-division player to one of the Bundesliga's most prodigious talents in two seasons with Dortmund, joined Manchester United at the end of last season.
Dortmund are also struggling to hold on to prolific Polish striker Robert Lewandowski.
"Mario has not in the slightest decided against his team mate or the club but he is a player of Pep Guardiola," said Klopp. "If there's anyone to blame, it is me but I cannot become 15 centimetres shorter and look like a Spaniard and play tika-taka football.
"He wants to have this chance to work with this outstanding coach; he did not want to miss it."
Bayern Munich, on the other hand, appear to be collecting top-class players at will and Goetze's move is likely to add to worries over their dominance in Germany.
The Bavarians have already wrapped up the Bundesliga title, reached the German Cup final and won their last two domestic games by 6-1 scorelines, despite fielding weakened teams.
Bayern, who signed Spanish midfielder Javi Martinez for 40 million euros at the start of this season, have won 18 of their 19 games in all competitions since the winter break, a run which included a 9-2 demolition of Hamburg SV.