Jenson Button says that Rubens Barrichello was a greater technical driver than the three fellow world champions – Jacques Villeneuve, Lewis Hamilton and Fernando Alonso – that he drove alongside in his Formula 1 career.
Button and Barrichello teamed up across four seasons at Honda and the title-winning Brawn GP squad that rose from its ashes.
The Briton was crowned champion that year before switching to McLaren, where Hamilton awaited and Alonso would later join.
While pointing out that both Hamilton and Alonso ranked highly among his 13 team-mates in F1, he said Barrichello's technical knowledge trumped the lot.
Asked for his top colleague, Button told F1's 'Beyond the Grid' podcast: "I don't know what 'best team-mate' means really.
"Fastest teammate would be Lewis and team-mate that was strong in every area would be Fernando.
"They all had weaknesses, as I had weaknesses, but they were both drivers that were remembered for their extreme talent and for their championships.
"The team-mate that I felt technically was above the rest, head and shoulders above the rest, would be Rubens – [he was] very talented when it came to setting up the car, I learned a lot from him.
"The one that surprised me the most was probably Checo [Perez], his speed and how on certain days he could be very quick.
"Circuits that had front limitation didn't work for him, circuits that had rear limitation like Bahrain worked very well for him and he was extremely quick. I don't know if he actually understood why it was but that's the way it was for him. To see how quick he was on circuits with rear limitation surprised me, and that surprised me more than any other team-mate, his speed on those circuits
"There's many drivers that had talents and skills that stood out, [but] there's not one really that I would say, 'He was the best by far'."