Nico Rosberg admitted he had to phone Mercedes boss Toto Wolff to tell him he was retiring because he could not tell his team boss about it in person.

Rosberg revealed on Friday that he had made his decision to retire from Formula 1 on Monday evening, after securing his first title in Abu Dhabi.

He then called Wolff to inform him of his decision, something he admits was incredibly hard to do.

"It was massively difficult," admitted Rosberg. "I couldn't tell him in person. I had to call him. It was massively intense especially after three hours of sleep."

Wolff said that Rosberg's reasons to leave the sport convinced him that his mind was made up.

He said: "It was a very difficult moment. We spent a day in Malaysia, with such a big crowd cheering for Nico, something I have never seen – it was unbelievable.

"We hopped on a flight from Kuala Lumpur to Singapore and from Singapore to Frankfurt and then we had some emotional discussions and he was so clear by what he said that he had no doubt about his decision."

Rosberg revealed that thoughts about quitting Formula 1 began when he won the Japanese Grand Prix, a victory that meant he did not need to win again to secure the crown.

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"This season, I tell you, it was so damn tough," Rosberg wrote on his Facebook page. "I pushed like crazy in every area after the disappointments of the last two years; they fuelled my motivation to levels I had never experienced before.

"And of course that had an impact on the ones I love, too – it was a whole family effort of sacrifice, putting everything behind our target.

"When I won the race in Suzuka, from the moment when the destiny of the title was in my own hands, the big pressure started and I began to think about ending my racing career if I became world champion.

"On Sunday morning in Abu Dhabi, I knew that it could be my last race and that feeling cleared my head before the start. I wanted to enjoy every part of the experience, knowing it might be the last time… and then the lights went out and I had the most intense 55 laps of my life."

Additional reporting by Jonathan Noble

Gallery: Rosberg told Wolff he is leaving by phone

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