Chelsea rounded off a whirlwind transfer window with the €12m signing of Pierre-Emerick Aubameyang from Barcelona, reuniting the striker with Thomas Tuchel, under whom he had thrived at Borussia Dortmund. Chelsea also strengthened in midfield with the season-long loan capture of Denis Zakaria from Juventus but announced in the early hours of Friday morning that defender Marcos Alonso had left the club by mutual consent. The Spaniard is expected to be announced as a Barcelona player on Friday after six years with Chelsea. The Aubameyang deal takes the London club’s outlay on incoming fees under the new co-owner Todd Boehly to more than £250m. “It’s an honour to be part of this team and I can’t wait to start,” Aubameyang said. “I have some unfinished business with the Premier League so it’s good to be back and really exciting.” It has been a frenetic summer with Boehly, acting as the sporting director, casting the net far and wide in an attempt to make his mark after taking over from Roman Abramovich and reshape the squad for Tuchel – especially after the departures on free transfers of Antonio Rüdiger and Andreas Christensen. The centre-halves moved to Real Madrid and Barcelona respectively after Chelsea could not offer them new contracts while Abramovich was under UK government sanctions. Chelsea have spent heavily on central defensive reinforcements, taking Kalidou Koulibaly from Napoli for £33.8m and Wesley Fofana from Leicester for £75m. A late bid for RB Leipzig’s Josko Gvardiol, worth £77.5m, was rejected, with the Croatia international extending his contract on Thursday until 2027. “Retweet and let everyone know: Josko Gvardiol is staying,” Leipzig announced. Chelsea could try again for him. Aubameyang is back in London, where he played for Arsenal – a four-year spell that burned brightly before imploding spectacularly over the first half of last season – and he is back with Tuchel. The manager had him for two seasons up to the summer of 2017 at Dortmund and enjoyed an excellent relationship with him, describing him as “a bit crazy but nice crazy”. Aubameyang scored 79 goals in 95 games under Tuchel in all competitions. Tuchel sanctioned the loan return of Romelu Lukaku to Internazionale in June and he has sought more flexible and mobile options up front, taking Raheem Sterling from Manchester City for £50m. Aubameyang adds further to the mix, able to operate centrally or off the left. Tuchel can also call upon Mason Mount and Kai Havertz, among others. Aubameyang had moved to Barcelona at the very end of last season’s winter window after being forced out of Arsenal by the manager, Mikel Arteta, and he scored 13 goals in 23 appearances for the club before the end of the campaign. The 33-year-old has barely featured this time out, making only one brief appearance off the substitutes’ bench as Xavi Hernández, the manager, has lent on his summer signings Robert Lewandowski and Raphinha. Aubameyang and his family were the targets of an armed burglary at their home in Barcelona last weekend. The thugs attacked Aubameyang, damaging his jaw – an injury that could delay his Chelsea debut. Tuchel had been keen for a new midfielder and, amid a flurry of bids for a clutch of players, he moved for Zakaria – the 25-year-old Switzerland international, who joined Juventus in January from Borussia Mönchengladbach. Chelsea have an option to make the loan permanent at the end of the season. Chelsea had made attempts to sign Edson Álvarez of Ajax, PSV Eindhoven’s Ibrahim Sangaré and Arsen Zakharyan of Dynamo Moscow, who has a £12.6m release clause. The Russian club released a statement in which they detailed the receipt of an offer from Chelsea and negotiations. “However, due to a number of technical reasons beyond our control, it is not possible to transfer the player this summer,” Dynamo added. “Nevertheless, our club remains open to proposals that will suit Dynamo and the player. At the moment, the parties have decided that Arsen will continue to play for Dynamo.” Alonso, who made 212 appearances for Chelsea across six seasons, is surplus to requirements after the £55m capture of Marc Cucurella from Brighton. Chelsea sent Ethan Ampadu to Spezia on loan, Kenedy to Real Valladolid and sold Billy Gilmour to Brighton.