Reluctantly I am forced to mention that my interpreter's fee should be at least doubled.

reluctantly 是副词，由形容词 reluctant（不情愿的）加上副词后缀 -ly 构成。reluctant 来自拉丁语 reluctari（抵抗、反对），表示"勉强的、不情愿的"。reluctantly 在句中修饰动词 mention，表示"不情愿地、勉强地"做某事。