The 55-year-old "Notting Hill" star said he doesn't know, who she is, when a partial image of the actress was shown on an online talk show and he was asked to identify her, reported AceShowbiz.
"Who is the one second from the right, because I've never seen her before in my life?," Grant said while referring to the "Jerry Maguire" actress' photo.
The actor got surprised after he was told that it was Zellweger's image.
Grant and Zellweger, 47, worked together in "Bridget Jones's Diary" (2001) and "Bridget Jones: The Edge of Reason" (2004).