In Italian, possessive adjectives normally require a definite article (like il mio libro or la mia casa). However, there is a very important exception: singular family members.
When you talk about a singular, immediate or extended family member using mio, tuo, suo, nostro, or vostro, you must drop the definite article.
Masculine Singular Relatives
Instead of saying il mio marito, you simply say mio marito.
This rule applies to all in-laws and extended relatives as well, such as cognato (brother-in-law) and suocero (father-in-law).
Feminine Singular Relatives
The same rule applies to feminine relatives like moglie (wife), nonna (grandmother), zia (aunt), cognata (sister-in-law), and suocera (mother-in-law).
Possession with "Di"
When you use the preposition di (of) to show possession—such as "my father-in-law's book", which is phrased in Italian as "the book of my father-in-law"—the zero-article rule still applies. Because there is no definite article before the family member, di does not combine into a joined word like del or della; it remains simply di.
