The 18-year-old split with 32-year-old Flack earlier in the year, and has since claimed "I'm not into cougars".
In an interview with The People, school friend Will Sweeney claimed: "I remember asking Harry about Caroline and he laughed.
"He said it was more of a physical relationship than anything else. All his mates think he's a bit of a legend though. It's classic Styles.
"He definitely enjoys the attention and he's making the most of it."
Sweeney also revealed that the singer has a soft spot for Katherine Schwarzenegger, daughter of Arnold, saying: "Harry just came out and said it one day. He thinks she's really nice."
One Direction bandmate Liam Payne recently suggested that Styles is "the biggest celeb flirt in the world".
Watch One Direction perform 'What Makes You Beautiful' on iCarly below: