Reeves appeared to confirm that he is in a relationship with artist Alexandra Grant during a red carpet appearance earlier this week, prompting support for the actor for bucking Hollywood trends and dating an “age-appropriate girlfriend”.
Many people took to Twitter to point out the physical similarities between Grant and Mirren, and the actor has now said she did not mind the comparisons.
"I saw that," Mirren told Entertainment Tonight. "That was very flattering on me, you know, because she's obviously lovely.
Mirren, who is married to director Taylor Hackford, added: "I do know Keanu very well. He did a film with my husband and he is just the most adorable, lovely person. So she's a lucky girl and I'm sure that he's a lucky boy."
Reeves and Grant have previously collaborated on books together, with the artist illustrating two of the actor’s works, Ode to Happiness and Shadows.
The pair also founded a publishing company called X Artists’ Books.