Formula One champion Nico Rosberg retires at 31.

Quitting at the top, Formula One champion Nico Rosberg shocked the world of motor racing Friday by announcing he was retiring at the age of 31, five days after earning his first world championship.

“I have decided to end my Formula One career. I had a very, very clear dream, that was to become Formula One world champion. I have achieved this childhood dream now and I am not willing to do that sort of commitment again,” Rosberg said in Vienna.

“So I have decided to follow my heart, and my heart has told me just to stop there, to call it a day.”

Rosberg said he made the decision Monday, a day after finishing second at the season-ending Abu Dhabi Grand Prix to clinch the F1 title.

“I am on the peak, so this feels right,” he said.

He wrote on Facebook of the difficulties he faced over a season that took a toll on people close to him: “It was a whole family effort of sacrifice, putting everything behind our target.”

Rosberg had a strained relationship with Mercedes teammate Lewis Hamilton. They came up through the karting circuits to became fierce rivals in F1, constantly needling each other in the media. They dueled for the F1 championship for the last three years. Rosberg was runner-up to Hamilton in 2014 and 2015, but hung on this year to relieve Hamilton of the title in the final race.

In an online video, Rosberg said: “I’m not willing to do it again next year.”

Rosberg won 23 races (tied for 12th all-time) and 30 pole positions (8th) from 206 races since his debut in 2006.

He began thinking of retirement after winning in Suzuka in early October, “when the destiny of the title was in my own hands.”

Mercedes chief Toto Wolff paid tribute to Rosberg for making a “brave decision.”

“He has chosen to leave at the pinnacle of his career, as world champion, having achieved his childhood dream,” Wolff said. “The clarity of his judgment meant I accepted his decision straight away when he told me.”