The Belgium international's move to Stamford Bridge was confirmed during the January transfer window, but he remained at Genk for the rest of the season and only linked up with the Blues earlier this month.
However, the intention was always to loan De Bruyne out for a year and Bremen have now confirmed the 21-year-old's arrival at Weserstadion, though adding that there is no option for a permanent transfer next summer.
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"We are pleased that we have been able to increase the quality in our squad with this deal."
Meanwhile, the versatile De Bruyne, who can also play out wide, is looking forward to playing regular first-team football with Thomas Schaaf's side.
"The move is perfect for me because Bremen has a great tradition and I'll be playing in full stadiums in one of the best leagues in Europe," the youngster enthused.
"Now I just want to show what I can do and be successful with my new team-mates."
The Blues starlet, who has been capped twice by his country, came through the youth-team ranks at Genk after being prised away from Gent as a teenager.