Kimi Raikkonen took part in an official GP3 development test at the Circuit de Catalunya in Spain on Friday.
The Lotus driver covered 58 laps with a best time of 1:34.780, which was over half a second short of the pole position time set in May's GP3 Spanish GP.
Raikkonen tested the car in order to give feedback on its behaviour as well as the different tyre compounds as the series is looking for ways to increase overtaking for next year's Championship.
Speaking about the test, the Finn said: "I wanted to test the GP3/13 because my friend Afa Heikkinen has a team [Koiranen GP] in this Series and I have been closely following their progress and results since the beginning of the season.
"I was curious to see how the car handled and it was actually fun to drive. There were a few issues regarding its behaviour, but we managed to solve most of them.
"The GP3/13 is a very good tool for young drivers, especially when you have to learn about tyre management like we have in F1."
GP3 Series technical director Didier Perrin praised Raikkonen's feedback, saying his experience was "invaluable".
"We are extremely pleased to have had the opportunity to work with Kimi," he said.
"His experience and feedback were invaluable and they gave us a better understanding of what needs to be done in order to make our car a better tool in overtaking opportunities for next season.
"He has confirmed all our hypothesis, and together we could start working on two development directions for the end of season testing. We would like to thank Kimi for testing with us and Koiranen GP for helping make this possible."