In the 15-second clip (below), the Glee star, who died on July 13, can be seen addressing a fan while seated on an airplane.
The Global News reports that the 31-year-old was flying from Japan to Vancouver in the video when he was asked by a flight attendant named Sheila to record a message to her boyfriend's daughter, Mallory.
In the clip, Montieth can be seen saying, "I wanted to record this video for you guys just to let you know to stay out of trouble and stay in school."
The star flew to his hometown of Vancouver on July 6 and checked into the Fairmont Pacific Rim Hotel. After catching up with friends and family during the week, his body was found in his room on the 21st floor of the hotel after he missed his noon checkout time on Saturday.
Monteith, who had battled substance abuse issues since the age of 12, spent a month in rehab in April.
He died of a "mixed drug toxicity" of heroin and alcohol, authorities say.
Fans of Monteith's may make donations in his name to three charities that were especially important to him: Project Limelight Society, which exposes youth living in Vancouver's Downtown Eastside to the arts; Virgin Unite, founded to support entrepreneurial efforts to better the world; and Chrysalis, which helps homeless and low-income individuals find employment.