A possessed pronoun in the Arabic language is attached to its possessor as a single word. The noun (ie the possessor) in this state becomes definite like a noun preceded by “ال” and therefore discards its tanween.

When the object(كتاب) for example, is owned by a boy in the third person state the possessive pronoun “ه” is used and it’s attached to the noun (book) to become “كتابه”.

The Arabic possessive pronouns