The 27-year-old actor was on her mind on Sunday, August 4 when she took to Instagram and posted a photo of Cole smoking a cigarette, adding a thoughtful caption.
She wrote: "I tried to find a poem/that I could send to you/Because my words were failing me/But I searched and found nothing that did you justice/All of these love poems can't get it right/No one else's words could ever fit/They haven't known the fortune it is to love you."
Lili called the piece "sappy nighttime birthday poem for @colesprouse."
She also wished his twin brother, Dylan Sprouse, a happy birthday on Instagram.
The notes came weeks after rumours of a split surfaced.
The "Riverdale" stars quickly addressed the gossip, while promoting their cover story for W magazine.
Reinhart wrote: "BREAKING: A reliable source has confirmed that none of you know s**t," alongside a photo of herself and Cole from the magazine shoot, while Sprouse added: "UNPRECEDENTED: Cole Sprouse and Lili Reinhart consume the flesh of 'reliable sources' to fuel their bacchanalian sex cult."
But the couple has yet to directly comment on status of the relationship, which began on the set of the teen drama.