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The "We're The Millers" star, who recently became engaged to actor Evan Peters, admits she can't get enough gossip about Styles and his bandmates and belts out their big hit in her car while driving around Hollywood.
She explains, "I'm blasting it in my car with the windows down (and) I'm lip syncing the whole thing, and I'm always scared I'm gonna pull up to, like, my friend's mom and she's gonna be like, 'Hey, what are you doing?'"
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She adds, "My little sister and I talk about One Direction all day. I'm scared if someone ever saw my phone; I'm like, 'Delete these messages' ... It's like, 'Harry Styles, Harry Styles, Harry Styles...' To all of my friends, it's like, 'What do you think Harry Styles is doing, do you think he's in L.A.?'"
But Roberts has gotten closer to her pop idol and his bandmates than most fans - she bumped into One Direction at an awards show.
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She adds, "I have, like, 100 selfies on my phone with all of them. Afterwards I was so embarrassed."
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