5-2 Possession with de

To express relationships or ownership...;

• use de(d') + [the noun or proper name]
• C'est le petit ami d'Élisabeth. That's Élisabeth's boyfriend.
  
• C'est le patit ami de ma soeur. That's my sister's boyfriend.
• *a more literal translation of those
  
• This/That is the boyfriend of Élisabeth.
• (or) It is (?) the boyfriend of my sister.

To Know...;

• de contracts when in front of the definite article le or les (the sing. or plur.). And obviously not la or l' (fem. or sing. def. art. when followed by a vowel starting noun/word)
  
• de + le = du of + the (sing. masc. def. art.)
  
• de + les = des of + the (plur. def. art.)
• *and remember the def. art. is dependent on the noun weather it is plur, sing, masc, or fem.