The "Hollaback Girl" singer continued her birthday wishes for her fellow Voice coach, positing another childhood photo of Shelton on her Instagram account.
"Happy birthday to @blakeshelton literally my favorite person," she captioned the shot.
Stefani signed both of her social media messages with her signature "gx" – known to mean "Gwen, with a kiss."
Earlier this month, Stefani set the record straight about all the "gossip-y, weird stories people make up" about her relationship with Shelton, telling 94.7 Fresh FM's "The Tommy Show" that she's taking their relationship "one day at a time."
Both musicians ended long-term relationships last year, with Shelton and Miranda Lambert divorcing in July and Stefani and husband Gavin Rossdale announcing their split several weeks later.
Shelton's birthday wasn't just filled with romantic messages. He also took time to congratulate friend Luke Bryan on his chart-topping song, "Huntin', Fishin' & Lovin' Every Day," tweeting him "Congrats @LukeBryanOnline on your #1 song... Even though you are a complete douche bag and a horrible influence on children.. And dumb."
"And ugly," he joked in another tweet.
"Just remember – I'll always be one month younger than your old ass," Bryan joked back.