Which line in this excerpt from Guy de Maupassant’s "The Necklace" reveals situational irony?
But one Sunday, having gone to take a walk in the Champs Elysees to refresh herself after the labors of the week, she suddenly perceived a woman who was leading a child. It was Madame Forestier, still young, still beautiful, still charming.

Madame Loisel felt moved. Should she speak to her? Yes, certainly. And now that she had paid, she would tell her all about it. Why not?

She went up.

"Good-day, Jeanne."

The other, astonished to be familiarly addressed by this plain good-wife, did not recognize her at all and stammered:

"But—madame!—I do not know——You must have mistaken."

"No. I am Mathilde Loisel."

Her friend uttered a cry.

"Oh, my poor Mathilde! How you are changed!"

"Yes, I have had a pretty hard life, since I last saw you, and great poverty—and that because of you!"

"Of me! How so?"

"Do you remember that diamond necklace you lent me to wear at the ministerial ball?"

"Yes. Well?"

"Well, I lost it."

"What do you mean? You brought it back."

"I brought you back another exactly like it. And it has taken us ten years to pay for it. You can understand that it was not easy for us, for us who had nothing. At last it is ended, and I am very glad."

Madame Forestier had stopped.

"You say that you bought a necklace of diamonds to replace mine?"

"Yes. You never noticed it, then! They were very similar."

And she smiled with a joy that was at once proud and ingenuous.

Madame Forestier, deeply moved, took her hands.

"Oh, my poor Mathilde! Why, my necklace was paste! It was worth at most only five hundred francs!"