His "Señorita" planted a fat one on him in front of friends during Mendes' 21st birthday celebration on Thursday.
The newly-linked couple showed their chemistry off-screen is just as hot with their very public makeout session.
Cabello can be seen grabbing the birthday boy's face as they lock lips. He quickly reciprocates the love by tightly grabbing his songbird girlfriend too.
The partygoers cheered as the duo passionately put their romance on display.
It appears the celebration went down in New York, just hours after the two were seen walking hand in hand around the city.
There's also video of Cabello and Mendes making intense eye contact during the party.
After his cake gets brought out, the pair's eyes are laser focused on each other and they appear to give off major "let's get out of here" vibes.
There is a blurry photos circulating too, showing Cabello hanging all over her birthday stud.
Rumors the two were romantically involved began earlier this summer, after fans noticed how much chemistry the superstars had in their music video, "Señorita."
Fans got even more excited when Cabello broke up with her longtime dating expert boyfriend weeks later.
Cabello and Mendes put the relationship speculation to bed when they were spotted with their tongues down each other's throats in Miami last month.
And it appears they're pretty serious, because she's already met some of his family.
Mendes' sister, Aaliyah, was spotted at last night's party and seen dancing with the famous pair.
The makeout session wasn't Mendes' only birthday surprise.
Cabello showed the singer some affection in a belated b-day post and even dropped the L-word.
"Happy birthday to this magic human, I love you!!!!" she wrote while posting an adorable couples pic.
Shawmila fans everywhere are completely losing it.