Landis was a key part of Armstrong’s US Postal (now Discovery Channel) team for three years before moving to Phonak.
“I’m proud and happy for Floyd,” said Armstrong, who watched the finish on TV from his hotel near the Champs-Elysées.
“He proved he was the strongest, when everybody wrote him off. I’m very proud that an American has won again.”
Armstrong joined his Discovery Channel team, of which he is a part-owner, at the beginning of last week before the Alpine stages.
Their highest finisher in his absence was Portuguese José Azevedo, 19th in the overall classification, 38 minutes adrift of Landis.