The 48-year-old singer and 41-year-old country star dressed up as Daphne and Shaggy while throwing Apollo, Stefani's youngest son with ex-husband Gavin Rossdale, a fourth birthday party Saturday.
Stefani wore a pink wig, purple dress and green scarf, while Shelton sported a messy blonde wig, green shirt and jeans. Apollo, who officially turns 4 on Wednesday, dressed as Scooby-Doo in a Great Dane onesie.
Apollo and his guests enjoyed a puppet show, bouncy castle and plenty of sweet treats. Stefani shared photos and videos on Instagram Stories throughout the bash, including a picture of herself and Shelton in costume.
Stefani has been accompanying Shelton on his Country Music Freaks tour. She shared a cute photo from Shelton's show Saturday in St. Louis, Mo., that shows the country star giving her a kiss as the moment is projected onscreen.
"#[heart] #countrymusicfreakstour2018 @blakeshelton #stlouismissouri gx," the singer captioned the picture.
Stefani and Shelton confirmed their relationship in November 2015 following their respective splits from Rossdale and Miranda Lambert. In addition to Apollo, Stefani and Rossdale share 11-year-old son Kingston and 9-year-old son Zuma.