Alexander Rossi admits that his race drive with Manor F1 came as a surprise, and says that the deal was put together so quickly that he only booked his flight to Singapore two days ago.
Rossi, who was a Marussia reserve driver last year, will contest five races that do not clash with his GP2 commitments.
The American replaces Spaniard Roberto Merhi at the team.
"I was on a plane Tuesday evening, and I booked the flight Tuesday morning," Rossi said on Thursday in Singapore.
"It was quite a last-minute thing. The discussions started taking place shortly after Monza.
"Obviously I've had quite a bit of history with this team, in '14, so we've always had good communication over the beginning of this year.
"But I wasn't expecting 2015 to be a year where I was racing an F1 car.
"My GP2 season is going very well and I feel very committed to Racing Engineering in that programme, and I'm very pleased that they kind of opened their doors and allowed me to do this programme, and at the same time a big thank you to Manor.
"Obviously it's difficult for them to have me in and then not in for a couple of races. It took work on both sides, and I'm very pleased and thankful that we were able to do it."
Inevitably his appointment at Manor has led to speculation that he will be in a stronger position with regard to a future drive with the American Haas team, even if it may already be too late for 2016.
"I think the big thing that I've been missing for the past three years in my F1 career is actually racing. We've been close quite a few times.
"It's very surreal now that it's about to happen. This is a major step in kind of really firmly putting myself on the F1 map and the radar, and I'm just focussing on doing a really good job in these five races, and showing that I am capable of being in F1 and doing a good job.
"My goal is to race full-time in F1, in whatever situation that is, in whatever situation that may present itself I'm going to jump at that with open arms.
"What this may lead to, I don't know. I'm hopeful that doing a good job in these five races will prove that belong here, and that I'm capable of doing it just as much as anyone else."
Regarding his target for the weekend, he said: "I think it's going to be a moving target. I haven't been in the car since Spa, of '14, so I'll just kind of being re-acclimatising. But it's not that much different to GP2, so I'm hoping to be on the pace quite quickly.
"It's be a learning experience, I think. You have to appreciate that you're here to do a job, but at the end of the day you're kind of only racing one other car, and you have to respect the others on track, so that will be something that I'll need to be very aware of.
"Through Friday and Saturday I'll get quite used to that, so I don't see it really being an issue."