The 81-year-old director was greeted with a resounding cheer and standing ovation when he stepped on the stage to give away the award to the veteran actress, according to The Hollywood Reporter.
Allen appeared towards the end of the evening to celebrate Keaton's work, who won her best actress Oscar for her starring role in and as 1977's "Annie Hall", directed by Allen.
The filmmaker also starred in the Academy Award-winning movie.
"We go back a long way, Diane and I," the director began his comedic monologue.
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They have acted together in number of films too.
Allen recalled how he was blown away by Keaton when he first met her because she came from Right-wing Orange County, having grown up in a town where "if you helped a blind person across the street, they accused you of Socialism".
Towards the end of the speech, he said, "Much of what I accomplished in my life I owe for sure to her".
After the address, Keaton went in to hug Allen and said, "Oh God, I just want to cry. Tonight has been an astonishing experience for me.