Luke, who portrayed Fred Andrews on the hit Netflix series, died aged just 52 in March after suffering a stroke, and the show will pay tribute to the actor and his character in the first episode of the upcoming fourth season.
Speaking during a panel discussion at Comic-Con in San Diego, California on Sunday (July 21), Roberto confessed he wanted to ensure he gave the star and his character a fitting send off because the show was so important to him.
"We suffered a huge, huge, huge loss and it's something we're going to be feeling for as long as we're lucky enough to keep making the show," he reflected. "I remember when Luke auditioned, he came up to me and said: 'I loved this script and when I read the character Fred, I liked him because he is just like me. I have a son and he is just like Archie.' Luke and Fred have many, many similarities."
Speaking with Entertainment Tonight ahead of the panel discussion on Saturday, he revealed more details about the "standalone" episode, adding: "It's going to reveal the fate of Fred Andrews and it's set on July 4th."
"It's a really emotional episode; it's a tear-jerker. We had the table read for it about (two weeks) ago and i'm not going to lie, we were all crying. But we think it, again, honours the memory of Luke (and) it honours the memory of Fred."
KJ Apa, 22, who plays Fred's son Archie, also revealed much of the upcoming season will centre on the Fred's absence, and the plot will "dip in and out" of the storyline through Archie's eyes.
"I think (we'll see) a lot of it through Archie's storyline," he shared. "I think that's a part of his storyline in season four, honouring his father's legacy."
Season four of "Riverdale" is expected to air later this year.