Lewis Hamilton refuses to accept 2019 was an easy year for him and Mercedes after the Brit cruised to a third successive Formula One title.
Hamilton wrapped up his sixth championship triumph with two races to spare after finishing second in the United States Grand Prix.
It saw Hamilton amass an unassailable 67-point advantage over Mercedes team-mate Valtteri Bottas.
However, Hamilton believes 2019 has been his toughest campaign in F1, despite having never looked in serious danger of losing his title, citing the death of Niki Lauder in May as another factor.
"No way has it been easy. It's been the hardest year for us as a team," Hamilton said, as reported by Crash.net. "We lost Niki this year.
"A crucial member and a real pivotal member of our team and the emotional rollercoaster that we've been on with losing him, and a race where I didn't have Bono [Pete Bonnington, Hamilton's race engineer] here, outside of the car, just trying to remain focused throughout the year.
"That is the toughest, and only other athletes who are at the top of their game can really, probably relate to it.
"This car has not been easy for us. We started the season honestly going off to Melbourne thinking that we were going to be behind.
"Mid-point of the season we were behind and it's been a real challenge, this second half of the season. It's been the toughest second half of the season that I think we've had as a team, fighting against Ferrari and Red Bull, which is great, we welcome that."
Meanwhile, Hamilton's father, Anthony, has challenged his 34-year-old son to race for another five or six years.
"Five to six years, that's where I'm pushing him," he told Channel 4. "I said to Lewis you just have to keep going for as long as you really enjoy it.
"And if your body can keep up with it, then great, but if you’re not enjoying it you know it’s time to leave, but he loves the sport."