Brazilian Formula One driver Felipe Massa announced on Thursday he will retire at the end of the 2016 season.
The 35-year-old, who began his Grand Prix career in 2002, confirmed his long-expected departure during a news conference ahead of this weekend's Italian Grand Prix at Monza.
"I'm more nervous now than for all my race starts," said Massa, who missed out on the championship to Britain's Lewis Hamilton by one point in 2008 at the final race of the season in his native Brazil.
"After 27 years of my racing career, since I started karting and with 15 years in F1, this will be my last season in F1.
"Life gives us so many choices. I think for me it has got to the time where I have to go and do something different."
Massa started his career with Sauber before moving to Ferrari in 2006 and then Williams.
He is in his third year with Williams, having joined the team in 2014, and will mark his 250th Grand Prix start at his final race in Abu Dhabi this year.
RAI (on Massa): "It's a big shame but his choice. We had a good relationship as team-mates. He's a very nice guy" pic.twitter.com/g7PcfvWQ74- Formula 1 (@F1) September 1, 2016
"Maybe you will see me again at the wheel of a race car, but at the moment the only certainty I have is that I will have a lot of time to decide on what I do in the future," the Brazilian added.
Massa, a winner of 11 Grands Prix, said he chose to make his announcement at Monza because former Ferrari team-mate and seven-time champion Michael Schumacher had done the same in 2006, thus confirming Massa's continued presence with Ferrari alongside Kimi Raikkonen in 2007.
"Ten years on from that day, and in the same paddock, I decided to announce my decision," he said.
Massa recovered from a serious head injury in 2009 when he was hit by a spring during the Hungarian Grand Prix.
He said he felt that his world title near-miss in 2008 was more due to events at the 'crash-gate' Singapore Grand Prix than anything else.
"Without that, I probably would have won the world championship," he said. "I know that I didn't make it for reasons that are not related to a driver error or a team problem. So it is more difficult to accept."
Massa added he was proud to have finished his career with Williams.
"I'm so proud to have been part of this team," he said. "Williams had a difficult moment and then we managed to get amazing results in the last two championships."
Deputy team principal Claire Williams was quick to pay tribute to the departing Massa.
"This is a very sad and emotional day. For Felipe, I know this was a big decision. He was so nervous," she said.
"He is what we love at Williams: a true gentleman. We were so lucky he joined for 2014.
"We were a team in dire straights. We needed someone to come and be part of the team."
Speculation in the paddock has linked 2009 world champion Jenson Button with a return to Williams, where he started his career, next season. He is currently with McLaren Honda.