The 23-year-old actor worked with him during the first season of Scream Queens.
“RIP Alan Thicke. Can’t believe it. Honor to have known you and to been able to work with you,” Patrick tweeted.
He also shared a photo of them together, captioning it, “RIP.” You can see that below.
Also pictured: Patrick stops by Barneys New York to do a little holiday shopping with his dad Arnold on Monday (December 20) in Beverly Hills, Calif.