It's one of her favorite passions - checking out the blog "Old Loves."
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But Lena Dunham was surprised when she saw someone familiar on the site that shows pictures of celebrity couples that have since broken up.
The "Girls" star saw her boyfriend Jack Antonoff, 29, with Scarlett Johansson, 29.
"Old Loves is my passion, I check it like once a week," she told Grantland last week. "I was going through it and I saw my boyfriend and his girlfriend from high school."
"Who was the girlfriend from high school?" host Bill Simmons asks.
"Scarlett Johansson," Dunham, 27, said casually. "I know I shouldn't have spilled that in a public forum, but you can Google it."
She added the couple was 17 years old at the time attending a school in New York City.
"I was like, 'My mind is going to explode.' I really did think I was hallucinating," she said. "It would be like seeing my parents."
Johansson is engaged to French journalist Romain Dauriac, and Dunham has been dating the Fun guitarist since 2012.