The Glee actress shared a black and white photo of the two laughing together along with a heartfelt caption.
"The biggest heart and most beautiful smile.. In all of our hearts..We love you so. Happy Birthday," Michele wrote about her late boyfriend who died last July at age 31.
The actress is still filled with love for Monteith and made sure her 4.3 million Twitter followers remembered him on his birthday, May 11.
Monteith was tragically found dead in a Vancouver hotel room.
His death came just months after he voluntarily checked himself into rehab for substance abuse.
In October of 2013, a coroner's report revealed that Monteith "died of mixed drug toxicity, involving intravenous heroin use combined with the ingestion of alcohol."
That same month, Glee paid tribute to the actor and his character in an episode titled "The Quarterback."