The 24-year-old singer and Davidson, also 24, appeared in a first photo together Wednesday following dating rumors.
Davidson shared a picture of himself and Grande wearing Harry Potter sweatshirts and house robes. The actor and comedian sported Gryffindor gear, while Grande wore Slytherin.
"The chamber of secrets has been opened," he captioned the post.
Grande was first linked to Davidson this month following her split from rapper Mac Miller. Davidson addressed his mental illness last week after fans suggested his borderline personality disorder makes his relationships toxic.
"normally I wouldn't comment on something like this ... but i been hearing a lot of 'people with bpd can't be in relationships' talk. i just wanna let you know that's not true," the Saturday Night Live star wrote.
"just because someone has a metal illness does not mean they can't be happy and in a relationship. it also doesn't mean that person makes the relationship toxic," he added.