The 21-year-old Belgian arrived at Stamford Bridge during the January transfer window and was immediately loaned back to former club Genk.
He made his Chelsea debut in the 4-2 friendly victory over Seattle Sounders during the recent tour to America, but Chelsea on Thursday confirmed he is to continue his development at Werder Bremen.
De Bruyne is determined to make a success of his time at Werder Bremen.
"It's good that the transfer to Bremen is now completed," he told the club's official website, www.werder.de.
"SV Werder have a big tradition and play in one of the best leagues in Europe with full stadiums all the time.
"I would like to prove successful with my new team-mates."
De Bruyne, who has been capped twice by Belgium, scored eight goals in 22 games upon his return to Genk.
Source: PA
Source: PA