Despite having an impressive debut campaign in Spain, Barcelona decided to part with Gundogan after struggling to register new signing Dani Olmo due to the club’s financial issues.
Gundogan was one of the club’s highest earners and his departure on a free transfer will help Barcelona comply with La Liga spending restrictions.
“I am leaving in a difficult situation, but if my departure can help the club financially, it makes me a bit less sad,” Gundogan wrote on Instagram following the announcement.
Gundogan added he had been “looking forward to helping my team-mates in the new campaign” but he was “grateful” to have spent 12 months at Barcelona.
Speaking ahead of Ipswich Town’s visit to Manchester on Saturday, Guardiola said the chance to re-sign the midfielder came out of the blue.
“It was a complete surprise, unexpected,” said Guardiola.
“We didn’t have any doubts when the possibility to re-sign him was open, and we’re absolutely delighted that he’s back.”
Capped 82 times for Germany, Gundogan announced his international retirement following the country’s Euro 2024 exit in the quarter-finals to Spain.