The five-time Emmy Award-winner died Sunday at the age of 90.
"Doris Roberts had an energy and a spirit that amazed me. She never stopped," Romano said in a statement to The Wrap Monday.
"Whether working professionally or with her many charities, or just nurturing and mentoring a green young comic trying to make it as an actor, she did everything with such a grand love for life and people and I will miss her dearly."
Heaton took to Twitter to express her grief over the death of Roberts, with whom she shared the screen on both ELR and The Middle.
"To my beloved Marie -- RIP. Truly the end of an era. My wonderful TV mother-in-law and ELR nemesis Doris Roberts was a consummate professional from whom I learned so much," the actress tweeted. "She was funny and tough and loved life, living it to the fullest. Nothing gave her greater joy than her three wonderful grandchildren, of whom she was so proud. It truly was a privilege Doris. I love you and miss you."
To my beloved Marie - RIP. pic.twitter.com/TtZCySQnLK— Patricia Heaton (@PatriciaHeaton) April 18, 2016