"Happy Birthday to this adorable pure soul who has reminded me what being happy feels like," Miller wrote alongside a photo of Grande giving the rapper a kiss on the cheek in front of the Eiffel Tower as Miller sticks out his tongue.
"Thank you for loving me so good. I think it's supposed to be "so well" but I don't care the 25-year-old continued. "I love you and can't wait for all of the adventures."
Grande confirmed she was dating Miller in September after the pair were spotted sharing a kiss in August. The couple have collaborated together on songs "The Way" and "My Favorite Part."
Miller has been by Grande's side following the suicide bombing in Manchester that killed 22 people and injured 49 others in May during a Grande concert. Us Weekly reported. Miller joined Grande for her One Love Manchester benefit concert that raised money for the victims and their families.