"Monaco Grand Prix — the race every driver looks forward to," he writes.
"When I look back now, what I will remember most about it is walking down to the paddock to meet with the media on the Wednesday before the weekend started, and receiving a bunch of questions about my future.
"Here I am, a handful of races into my F1 career, and I'm being asked about the end.
"The worst part of that day, though, was finding out there was some truth to the rumours.
"After a few races, there were some people, it appeared, who didn't want me there. I'll be honest, this was a bit of a shock. "
Hartley said he was stunned to find that after all of his other racing success "there was talk of my being replaced so early".
Hartley writes: "That's life in F1, though. The sport has so much money and so many people involved, it's only natural that there are politics. If you're a fan you know it, and if you're a driver, you live it.
"…the way I responded, the way I put my head down and kept going — that's one of the things I'm most proud of this season.
"…going into Abu Dhabi, I knew that no matter what happened after the race I would leave the circuit with my head held high.
"But, like the fans, I had no idea what was going to happen. That's the thing about the politics in F1, it can be a little bit … awkward.
"Everyone sort of walks on eggshells, and there isn't always clarity. So I just did all I could: my job. I out-qualified my teammate and drove to 12th on Sunday night.
"An hour later, I was summoned to a meeting. And a few minutes after that, I was no longer an F1 driver.
"I went back to my driver's room, I hugged (wife) Sarah. There were some tears, some sadness, but also already looking to the future and the next steps.
"It was clear to me then that from as far back as Monaco there was a plan in motion to move me on.
"That was it. What I thought didn't matter."
Hartley also suggests he felt part of a Kiwi jinx.
"After the midway mark of the season I couldn't help but think of my fellow Kiwi Chris Amon, who had been dubbed the "Most Unlucky Driver in F1 History," Hartley writes.
"What is it about Kiwis in F1?
"From hitting birds, being taken out on the first laps, engine penalties, suspension failures and other issues that weren't always mentioned in public, it felt like I was going down the same path."
Hartley lost his Toro Rosso seat to Formula 2 driver Alexander Albon for this year.
