The Emmy Award nominee, 49, raved that Olsen, 33, is "truly an inspiration" to her as she spoke about their friendship and introduced the Scarlet Witch actress at Variety's Power of Women event on Wednesday in Los Angeles.
"First of all, she was my intro into this Marvel family and she very generously walked me through blasts and wires and stunts and finding truth on an X on a green screen. I was used to talking to other people," Hahn said, before joking: "She was so patient with all of my questions: Who was Ultron? What is that glove with all the gems on it?"
She continued: "But she was very patient with me as it took me like a solid 40 minutes to 10-one which ... is to urinate in the movie business. I have a lot of costume on and a very small bladder."
Hahn made her MCU debut last year in Disney+'s WandaVision, playing powerful and manipulative witch Agatha Harkness, the antagonist to Olsen's Wanda Maximoff.
courtesy of Marvel Studios
As filming on the series halted during the onset of the COVID-19 pandemic in March 2020, the costars continued to have each other's backs.
"In the heart of lockdown, she brought worms from her garden over to us to compost," she recalled. "And my husband, for some reason, it was really important for him to make sure that she knew that they're thriving. So Lizzie, just know that they're alive and well.
"And did I hand her a loaf of bread in return that was clearly store-bought? Yes. She graciously accepted. And did she and her husband write and record a song for me as my wrap gift for WandaVision? Yes. And is it as perfectly strange and hilarious and singular as I ever dreamed of it being? Absolutely," Hahn added.
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When asked if she'd reprise her role as Agatha for another title in the franchise, Hahn told PEOPLE last April: "Of course, I would! I would love to. Yeah, absolutely."
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Although she added that she has "no idea" if the opportunity will arise, noting that Marvel "runs a real tight ship," a dark comedy spinoff for Agatha was reportedly in development at Disney+ as of October 2022.