Hours after news of Salling’s death broke, Morrison, who starred as Will Schuester on the hit Fox show from 2009-15, paid tribute to the actor on social media.
Morrison, 39, shared a touching throwback photo of himself, Salling and late Glee castmate Cory Monteith — who died at the age of 31 in 2013 from a mixture of heroin and alcohol — that was taken during a PEOPLE photo shoot in 2009.
In the image, Monteith is on the left, Morrison is in the center and Salling is on the right; each sport black suits, ties and an unbuttoned white shirt. Morrison captioned the photo with three simple emojis (😇😔😇): two angel faces — which represent Monteith and Salling — flanking a sad face, representing Morrison.
Jenna Ushkowitz, who played Tina Cohen-Chang on the musical dramedy, also expressed her sadness about Salling’s passing by leaving a red heart emoji in the comments section.
And Jane Lynch — Glee‘s Sue Sylvester — shared her condolences by retweeting Glee producer Tim Davis : “Let me be clear. Having compassion for #MarkSalling in no way minimizes his crimes, nor does it minimize the pain and devastation of the victims of those crimes. I’m just saying stop adding to his family’s pain. This was their son. If you’re without sin, feel free to cast stones.”
WATCH: Glee Star Mark Salling Pleads Guilty to Possession of Child Pornography
Salling’s death comes about a month before he was scheduled to be sentenced to prison for possession of child pornography.
The Glee star pleaded guilty to possession of child pornography involving a prepubescent minor Oct. 4, 2017. After striking a plea deal in December, he was due to be sentenced in March and expected to serve four to seven years in prison.
“Mark is focused on accepting responsibility and attempting to atone for his conduct,” his attorney, Michael Proctor, said in a statement to PEOPLE at the time.
Proctor said in a statement Tuesday that “Mark was a gentle and loving person, a person of great creativity, who was doing his best to atone for some serious mistakes and errors of judgment.”
Salling is survived by his mother, father and brother.