The pair both graduated from the famed Clairefontaine academy and formed part of the France squad which won the 2003 Confederations Cup.
And, with the duo set to be reunited as Andre Villas-Boas' men continue their American tour, Gallas revealed their long-standing friendship.
"It will be nice to see [Henry] again," Gallas told Goal.com after Tottenham's 0-0 draw against Liverpool on Saturday.
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"I've known him for a long time, since I was 13 years old. He was one of the best strikers in the world and now he's in America so all I can say is everyone respects what he did in football."
The 34-year-old also recalled Henry's reaction to the news that he was set to sign for the Gunners' north London rivals Tottenham.
"You know he was a big star for Arsenal. When I signed for Tottenham, he told me 'commitment, you know' it was very funny," Gallas said.