In a video interview, actress and U.N. Goodwill Ambassador Emma Watson gets education activist and Nobel Peace Prize winner Malala Yousafzai to do something she's never done before: call herself a feminist.

The moment came in a live Q&A posted on Watson's Facebook page. The video, which was promoting Yousafzai's film "He Named Me Malala," has gone viral with 4 million views in just two days. In the interview, Yousafzai tells Watson that her September 2014 #HeForShe speech, which called on men to support gender equality, inspired her to embrace the term.

"This word, feminism, it has been a very tricky word. When I heard it the first time, I heard some negative responses and some positive ones," Yousafzai says in the video.

"I hesitated in saying am I a feminist or not and then after hearing your speech, when you said 'if not now, when? If not me, who?' I decided that there's no way and there's nothing wrong by calling yourself a feminist, so I am a feminist. And feminism is another word for equality."

In her Facebook post, Watson describes that exchange as the most moving of the day.

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