Madame Forestier is called up out the blue by Mathilde. She would like to come over for a bit.
Mathilde asks if she can borrow some jewelry from Madame Forestier.
You did this to me!
As Mathilde looks through the jewelry, she realizes that she doesn't like anything that Madame Forestier had shown her thus far.
Madame Forestier hoped and hoped that Mathilde wouldn't realize that the necklace was fake before she returned it to the ball.
10 years later. Mathilde screams from across the street. "You did this to me! It's you're fault I'm old and wrinkly now. You lent me the necklace and when I lost it, i had to buy a new one and it cost 36000 francs!"
In that moment, Madame Forestier realized that it was time to tell Mathilde the truth. "The daimond necklace was only 500 francs at the most. It was a faux." She would never forget the look on Mathilde's face when she said that.