The two stars' characters in 1992 movie 'Dracula' got hitched and the 52-year-old actress previously revealed their union was technically the real deal after director Francis Ford Coppola hired a real Romanian priest for the scene.
And though the pair are in relationships with Scott Mackinlay Hahn and Alexandra Grant respectively, they still value the bond they have with one another.
Winona, 52, was asked on the 'Happy Sad Confused' podcast how the "two biggest luddites on the planet" manage to keep in touch and she replied: "I know.
"But we do text, and we always say who it is, even though it says it on the text ... On his birthday, when I'm like, 'Happy Birthday, my husband!' and I put 'Noni,' he's like, 'Hey, wife! Love you, KR 57.'
"On each birthday he's like, 'KR 57' or whatever his age is.
"He's always done that."
Keanu, 60, previously declared he and Winona are "married under the eyes of God".
The two stars' characters in 1992 movie 'Dracula' got hitched and the actress previously revealed their union was technically the real deal after director
Speaking in a video interview with Esquire, he said: "We did a whole take of a marriage ceremony with real priests.
"Winona says we are. Coppola says we are.
"So I guess we're married under the eyes of God."
Winona claimed in 2018 she and Keanu were married.
She said at the time: "We actually got married in 'Dracula'. No, I swear to god I think we're married in real life.
"In that scene, Francis [Ford Coppola] used a real Romanian priest. We shot the master and he did the whole thing. So I think we're married."
And around the same time, the 'Stranger Things' actress admitted she has always had a playful soft spot for her co-star.
During a joint interview, she said: "I had a pretty big healthy crush on him."
Keanu replied: "I had a big healthy crush on you too."