Holtzbrinck Publishing Group is the name given to the publishing division of the Holtzbrinck Group, a German media conglomerate.
The Holtzbrinck Group was founded in 1840 by Friedrich Carl von Holtzbrinck in Stuttgart, Germany. The company initially focused on printing, but later expanded into publishing.
Therefore, while there isn't a specific date for the creation of Holtzbrinck Publishing Group, it is a division of the Holtzbrinck Group, which was founded in 1840.