The 'Terminator' star reached the milestone birthday on Sunday, and in a snippet of a speech given at the star's celebratory bash, fellow Hollywood veteran Sylvester, 71, took a moment to praise his "boundless energy".
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In the video clip posted on Instagram, Sylvester said: "You're so great, because you don't quit. You don't quit, and you still don't quit. And really it's boundless energy. But you've been a fantastic enemy, and a better friend, and that's all I can say."
And although the clip is only short, the 'Rocky' star assured fans it was only "a little bit" of his supposedly much lengthier speech to his pal.