To celebrate the pop star's special day, Shelton, 44, took to Instagram on Saturday, sharing a loving photo of himself and Stefani in a cornfield, cuddled up while the country crooner strums a guitar.
The shot appears to be a still from their music "Happy Anywhere" music video.
"It’s a special day for a special lady in my life," wrote Shelton in the caption. "Happy birthday @gwenstefani, I’d write a song for you every single day if I could..."
The pair already share a number of songs beyond "Happy Anywhere."
Stefani and Shelton also duet on the tracks "Go Ahead And Break My Heart," "You Make It Feel Like Christmas" and "Nobody But You."
At the Academy of Country Music Awards last month, Shelton bagged the award for single of the year for “God’s Country," and also used his acceptance speech as an opportunity to gush over Stefani.
Shelton thanked the "Hollaback Girl" singer for "encouraging me" and "for being my inspiration."
“Thank you God!" the country star added from Los Angeles.
Shelton and Stefani also performed at this year’s awards ceremony with a duet of their single “Happy Anywhere” which they played on a green-screened Bluebird Cafe.
Fox News' Julius Young contributed to this report