"I have lost a real friend," he added. "My life " and this country " is better for his being in it." Newman, who died on Friday aged 83, first starred alongside Redford in the 1969 "Butch Cassidy", the much-loved Western about two outlaws on the run.
While Newman was already established as a Hollywood star, the film is widely regarded as being the movie that catapulted Redford to the big time. The movie also marked the beginning of an off-screen friendship spanning some five decades. The two men reunited for the Oscar-winning 1973 film "The Sting" where they played two con-men planning to avenge a friend's death.
"Certain friendships are too good and too strong to talk about," Redford once said of Newman.
The two men had hoped to make one last movie together, an adaptation of Bill Bryson's "A Walk in the Woods" but were forced to scrap the plans because of Newman's advanced years.
"I got the rights to the movie four years ago, and we couldn't decide if we were too old to do it. Then we decided, 'Let's go for it," Redford said in a 2007 interview. "But time passed, and Paul's been getting old fast. I think things deteriorated for him. Finally, two months ago he called and said, 'I gotta retire.' The picture was written and everything. It breaks my heart."