Fernando Alonso sent a warning to his rivals by setting the fastest lap time at Formula One's post-season test in Abu Dhabi on Tuesday.
The two-time world champion will return to the grid with the rebranded Alpine team (currently Renault) next season after two years away from the sport.
His participation in Tuesday's test was controversial as the session was originally scheduled for young drivers with experience of less than two races in F1.
Alonso, who is 39 years old and has started 311 grands prix in his career, was given special dispensation by the FIA to take part in order to get his first full day of testing in a 2020-spec car.
He briefly drove this year's Renault R.S.20 at a filming day in October but was limited to 100km, while the rest of his preparation for his return has been in a 2018-spec car to comply with F1's strict testing regulations.
He completed 105 laps on Tuesday, over 583km or nearly two race distances, setting a fastest time of 1:36.333 on Pirelli's softest compound tyre.
Comparisons to Saturday's qualifying are not perfect due to different track conditions, but for context Max Verstappen's pole time was a 1:35.246 and Alonso's teammate for next year, Esteban Ocon, set a 1:36.359 in the same car.
Renault confirmed Alonso completed low-fuel qualifying-style runs as well as a race simulation in order to get up to speed with the latest F1 machinery.
"It was good and very nice to be back in the car especially with the race team," Alonso said. "I've been testing the 2018 car in preparation but this one felt a bit more serious and it ignited a little bit the competitive spirit.
"It was great to feel the modern cars and experience what they can do. I was watching the team's progress at the weekend closely and it was nice to experience what I learnt from the outside and then inside the cockpit today.
"We signed off lots of basic things we did in preparation at the factory like seat fitting, pedal position and so on, which is beneficial with only one and a half days of winter testing next year.
"We ticked boxes today and we go into Christmas and New Year with good spirit and everyone motivated in the team."
Teams were allowed to run two cars at the test and world champions Mercedes finished the session second and third.
Mercedes' Formula E drivers, Nyck de Vries and Stoffel Vandoorne, were driving the 13-time race winning W11, with respective lap times of 1:36.595 and 1:36.840.
Alfa Romeo reserve driver Robert Kubica, who also would not have met the original entry requirements for the test, was fourth fastest, albeit over a second off Alonso's fastest time.
There was also a glimpse of next year's driver line-ups, with Yuki Tsunoda, who is expected to be confirmed as Daniil Kvyat's replacement at Alpha Tauri, fourth fastest and Mick Schumacher, the son of seven-time world champion Michael, 15th fastest with 125 laps in the Haas.
McLaren and Racing Point opted against taking part in the test and Haas decided to run just one car instead of two.
For the most part, reserve and junior drivers took part, with drivers who raced regularly in 2020 ruled out of running by the FIA.
Times and lap counts
1. Alonso, Renault, 1:36.333, 105 laps
2. De Vries, Mercedes, 1:36.595, 110 laps
3. Vandoorne, Mercedes, 1:36.840, 82 laps
4. Kubica, Alfa Romeo, 1:37.446, 89 laps
5. Tsunoda, AlphaTauri, 1:37.557, 123 laps
6. Vips, Red Bull, 1:37.770, 101 laps
7. Fuoco, Ferrari, 1:37.817, 126 laps
8. Ilott, Alfa Romeo, 1:37.826, 93 laps
9. Zhou, Renault, 1:37.902, 98 laps
10. Aitken, Williams, 1:38.153, 78 laps
11. Shwartzman, Ferrari, 1:38.157, 129 laps
12. Buemi, Red Bull, 77 laps
13. Sato, AlphaTauri, 1:38.495, 127 laps
14. Nissany, Williams, 1:39.800, 75 laps
15. Schumacher, Haas, 1:39.947, 125 laps