British pop icon Harry Styles has run under the radar to complete the Berlin Marathon in a smoking time.

The One Direction singer used the pseudonym Sted Sarandos to charge over the finish line of the 42.2-kilometre race in less than three hours.

His official time was 2:59:13, besting his achievement at the Tokyo Marathon in March when he ran a still respectable three hours and 24 minutes.

Styles blended into the packed field of 50,000 runners wearing a black long-sleeved running shirt and black shorts, a sweat band and sunglasses.

His running shoe of choice was the fluorescent pink Nike Alphafly 3 — featuring a carbon plate for spring.

Styles’ running bib with race No.31261 was pinned to his chest.

Spectators lining Berlin’s streets couldn’t believe their luck when the Watermelon Sugar singer wizzed past.

“Rumour has it Harry Styles ran a sub-3 marathon in Berlin… not sure if anyone’s heard of it?” posted marathon organisers on Facebook.

Styles posed for a photo with double amputee and Paralympic gold medalist Richard Whitehead, who posted: “2.58 in Berlin with my mate!! Anyone know him!!”

Achieving a sub-three-hour marathon is a goal for many runners and can take years to achieve, with very focused training.

It requires running the race at a pace of 4.15 minutes per kilometre.

The Berlin Marathon is considered one of the fastest in the world. Eight previous men’s world records were all run in Berlin.