The former couple may have rekindled their romance because they were seen kissing at a Starbucks in North Hollywood on Wednesday.
"They were walking toward Starbucks," an onlooker tells PEOPLE. "Then the next thing we knew, he grabbed the back of her head and started passionately kissing her on the side of the street."
A healthy-looking Hill, who wore jeans and a blue T-shirt, and Klein, who wore a black tank top and a floral skirt, walked into the Starbucks together where they ordered a latte, two iced coffees, bagels and cream cheese.
But even a caffeine fix couldn't curb their passion.
"As soon as they sat down they started kissing again," the source added. "They were so into each other, it was like there was nobody else in the store, actually I think they forgot where they were, it went on for at least five minutes."
Hill, who moved to Los Angeles last month, dated Klein for approximately four years, before they reportedly split back in October 2011.
Moving back to LA in 8 days. What should I do first?— Jonah Hill (@JonahHill) April 22, 2013
– Raha Lewis