Sir Jackie Stewart has paid tribute to his on-track rival and friend Sir Jack Brabham, the three-time Formula One world champion who has died aged 88.
Australian Brabham passed away at his home on the Gold Coast on Monday morning.
He won the F1 world title in 1959 and 1960 with the Cooper team and in 1966 in a car he had manufactured himself, the Brabham BT19, as well as taking the constructors' crown in 1967.
And Stewart - another three-time F1 title winner, with the first coming in 1969, Brabham's penultimate season before retiring - said: "It is a great loss to motorsport that Jack Brabham has died.
"He died peacefully and unexpectedly, although he had been ill for some time. I saw him this year in Australia and we had a good chat.
"Jack was a fierce competitor and a modest and almost shy man, but a great three-time world champion who accomplished more than any other driver in the history of grand prix racing.
"Not only did he win the world championship three times, but he won driving his own car, which is a feat I suspect will never be matched.
"He was an extremely talented driver and very deceptively fast. He was also a very aggressive driver and probably one of the most difficult men to overtake - never apparently blocking intentionally, but somehow or other he was incredibly difficult to pass.
"He was a tough, hard driver and a hugely important part of motor-racing history. I am very fortunate to have been able to call him a friend and I am glad to have lived in the era of Jack Brabham.
"The entire Stewart family sends our condolences and sympathy to (Brabham's wife) Margaret, his sons and his grandchildren."
Sir Stirling Moss, who competed against Brabham in the 1950s and 60s, told BBC Radio Five Live: ''My career would have been considerably less without him.
''Every race - and I'm talking 50-odd times a year - we would fight against each other.
''I remember in New Zealand in the early 50s, we were contending the New Zealand Grand Prix or something like that, and I had a problem with my back axle.
''The first person that came up was Jack and he said 'take it off my spare car', knowing very well that there was a good chance I might beat him.
''That sums him up to me - a real sportsman and a good Aussie.''
Brabham's 1966 win has been described as ''an extraordinary achievement'' by compatriot Alan Jones, the 1980 drivers' champion, who added: ''We have lost an iconic Australian sportsperson and a great inspiration to all of us.
''He was very inspirational to me - he taught me that I could pack my bags and go to the other side of the earth and if I tried hard enough, I could achieve my dream, which is exactly what Sir Jack did.
''He is one of the true great sporting entities of Australia, with (Don) Bradman and Rod Laver and a few of those guys - I think Jack's right up there.''
McLaren executive chairman Ron Dennis also paid tribute to Brabham, who he described as a ''legend''.
Dennis said: ''He remains the only driver to win a Formula One world championship driving a car bearing his own name - a unique achievement that will surely never be matched.
''When I started out in Formula One in the late 1960s, I worked first for Cooper and then for Brabham. Even as a callow youth, I could recognise greatness when I saw it, and I'll always regard it as an honour and a privilege to have worked for Sir Jack. I learned a lot from him too.
''So, on behalf of all at McLaren, I'd like to pay tribute to one of the most illustrious names in motor racing history, and above all to extend heartfelt condolences to Sir Jack's widow Margaret and his three sons Geoff, David and Gary.
''Sir Jack Brabham, legend, RIP.''
Current F1 drivers took to Twitter to pay tribute, with Lewis Hamilton writing: "RIP Sir Jack Brabham. What an amazing driver and man #legend."
Australia's Red Bull racer Daniel Ricciardo wrote: "Sorry to hear about Sir Jack Brabham. A great Australian who inspired many Aussies to pursue our dreams."
Meanwhile, fellow Australian Mark Webber, who retired from F1 last year, said on his official website: "I was saddened to hear the news of Jack's passing today - he is the epitome of a champion racing driver and a true blue Aussie.
"He was a trailblazer; he took the hardest road and made it easier for the rest of us to follow.
"What he achieved taking on the best in the world and winning one of his three world titles in his own machinery is the stuff of pure legends.
"To Margaret, Geoff, Gary and David and their respective families, you are very much in our thoughts at this sad time. Jack was a legend in the truest sense of the word, an inspirational Aussie battler and someone who will never be forgotten."