The star, real name Dominic Harrison, turned 22 on Monday (August 05), and the "Bad at Love" singer took to Instagram to show him some love.
"darling dom. everyone who has met you in this life, for any amount of time at all, will be changed forever because of it," she gushed.
"for some, in small ways they won't even realize. for others, in a life changing wave. and every single one of them will be better, from having crossed your path for even a second. you leave an irrevocable shine on every soul you come in contact with. mine is gleaming. happy birthday, I love you."
The couple began dating earlier this year, after 24-year-old Halsey sent YUNGBLUD a direct message with her phone number.
The pair took their romance to the stage at the 2019 iHeartRadio Wango Tango concert in June with a steamy performance of their "11 Minutes" collaboration.
"I brought a friend with me tonight," she told fans at the gig in Carson, California. "How many people are here tonight with someone you love?"
YUNGBLUD then took the stage with a guitar as his girlfriend gyrated in front of him.