Jimmie Johnson says the hardest aspect of his "worst" NASCAR Cup series season was working through the 2018 campaign knowing he was parting with crew chief Chad Knaus.
Since his Cup series career began in 2002, Johnson had his first winless season this year, and only truly contended for victory once.
He collided with Martin Truex Jr on in the final corner of the last lap of the Charlotte Roval race and was then had his attempted overtake labelled as "desperate" by the then-Furniture Row Racing driver.
Johnson also contended with the loss of his long-time backers Lowes, signing a replacement late in the year, but says deciding the split with Knaus mid-season was the biggest obstacle in his year.
"In my Cup career that is probably the most difficult year that I have had," he said.
"I can look back at some other years where I had different challenges of not having a sponsor or maybe not having a ride and dealing with adversity there.
"As far as having a fully funded high-qualify ride, 2018 was by far the toughest. [A failed title defence in] 2015 was pretty tough, but this was still tougher than that.
"Especially, to work through the decision to go separate ways with Chad.
"Early in the year, kind of mid-season when we made that decision and working through that scenario wasn't easy.
"I've got a lot of work to do with my new team, we've got a lot of work to do with this new package and we've got to come out stronger."
Expanding on the loss of Knaus, Johnson said: "You know it's time for us to move on and have a new project and have new people to work with. But he is my brother, there is just no way around it.
"So, it's not an easy situation. It sure has not been easy, especially the second half of the year.
"We knew this was coming prior to the announcement, I should say, but the season is behind us now and I look forward to a good off-season and get geared up for 2019."