The 27-year-old "Slide Away" hitmaker has been dating Cody since October (2019), and took to her Instagram Stories to send him a sweet birthday message.
"Happy birthday to my favourite human to get weird with on the entire earth," she penned, alongside a video of the two of them wearing face masks.
Miley's message came a day after she explained she wouldn't be able to celebrate with her man on his actual birthday, as he would be in Milan, Italy, attending the Armani fashion show.
As an early present, Miley gave Cody a personalised vintage doctor's bag that was inscribed with the words "Prince Neptune" – a reference to his upcoming book of poetry and prose, which drops in April.
Meanwhile, Miley is in the midst of divorce proceedings with "The Hunger Games" actor Liam Hemsworth, from whom she split in August last year after eight months of marriage. The singer reportedly filed papers after reaching an agreement with her ex on Christmas Eve (December, 24 2019).