The Tophane Treaty of April 5 (new style: March 24th) 1886, signed in the Tophane Palace in Istanbul (the photo above), appointed the formerly autonomous region of East Roumelia to be governed from then on by the Bulgarian knyaz Alexander of Battenberg. The area of Tumrash (which since before 1885 was not in the administrative management of Plovdiv) and the Kurdzhali canton (region) with a total territory of 1640 sq.km. were taken away from East Roumelia in favor of the Ottoman Empire. After the recognition of the Unification of Bulgaria, its territory actually increased to 96 346 sq.km.
More info on that period of BG history – here and here