Harry Styles just time-traveled to the 1970s -- stepping out in London, looking effortlessly cool on a low-key stroll.

The former 1D heartthrob rocked some serious sideburns and a ’stache, casually flexing a blue tote from his own lifestyle brand, Pleasing, and sipping what looked like a matcha Wednesday.

Despite being an A-lister, Harry wasn’t exactly mobbed by fans -- guess he knows London’s got a way chiller vibe than flashy Hollywood.

Still, with that signature style, you knew he was someone major -- effortlessly owning the off-duty look as he strolled along, drink in one hand, EarPods inserted.

Of course, catching Harry in casual mode is a rare treat -- he’s booked and busy, while fans are hanging onto every crumb about his highly anticipated fourth album.