Nico Rosberg has revealed he sent an email of admiration to former team Mercedes after George Russell's maiden F1 victory at the São Paulo Grand Prix.
The German won the 2016 world championship with the Silver Arrows before announcing a shock retirement that winter.
Mercedes had dominated F1 from 2014 until last season, where Max Verstappen ended the monopoly by securing his first drivers' championship, though the German manufacturer still triumphed in the constructors' standings.
But the regulation changes set the Brackley-based team back compared to Red Bull and Ferrari this year, with Russell and Lewis Hamilton struggling to match the pace of their rivals.
The pain was ended at the penultimate round, however, when Russell secured victory in the sprint before taking a commanding win ahead of Hamilton in a Mercedes one-two at Interlagos.
Speaking to Sky Sports' Any Driven Monday, Rosberg said: "I wrote them an email, my ex-colleagues in the team to congratulate them and say how incredible it was and also congratulating them on their driver line-up.
"I think they have such a strong driver line-up.
"Lewis is still at his very best and yet George is always there, right next to Lewis, a little bit in front or a little bit behind so they are so closely matched.
"I think the driver line-up is so strong."