Robert Kubica has admitted choosing Williams over a development driver role at Ferrari in 2019 was "not easy".

Just as the speculation began to pick up that the Pole was favourite to land the race seat with the Grove-based squad, it emerged he had been offered a position replacing Daniil Kvyat and Antonio Giovinazzi behind the scenes at the Scuderia.

The deal put forward was also reportedly longer than the one year he has with Williams but ultimately, one key factor was crucial in Kubica's decision.

"I had some opportunity which I think was very interesting and it was not easy to say no," he told Autosport.

"In the end, I am a racing driver - even though I haven't been racing for quite a long time - and this racing mentality has won out.

"I'm happy to have made this decision because it is a big challenge."

Looking ahead to this upcoming season, Kubica is proud to have achieved his goal of returning and is keen to see how it plays out.

"It's not easy to become an F1 driver: it's not easy to convince people you can do it and establish yourself in an F1 paddock," he explained.

"You have to have a lot of drive to do it because I went through this 12 years ago, and in the end, I said I think I have the energy to do it again.

"I'm not worried or scared of this challenge and I think I can make it work.

"I have a great opportunity and it is a happy ending to the long journey I have been on."

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The 34-year-old then ended by talking about some of the differences he'll face in transitioning from a test driver role to that of a racer.

"When I was driving the car I had to keep in mind that I have to give quality information and feedback and that I'm able to deliver good pace and not risk anything," Kubica said.

"I have to change this approach a bit because now I have to work more for a team, as I was, but now also for myself.

"I need to focus on different things which might be useful when I am racing. It's a bit of a different approach."