Joanna attended her high school reunion. she was surprised at how easily she and her old friends bonded. she could not but think that the more things change, the more they stay the same. which literary device did the author use in the passage?

In the passage, "Joanna attended her high school reunion. She was surprised at how easily she and her old friends bonded. She could not help but think that the more things change, the more they stay the same. ", the literary device that the author used is irony.