'My heart is breaking,' wrote Bonnie's onscreen daughter Valerie Bertinelli in a touching memorial on her website.
'Bonnie has always been one of the most important women in my life and was a second mother to me. The years on One Day At A Time were some of the happiest of my life, and along with Pat and Mackenzie we were a family in every way.'
'My heart is breaking': Since the tragic news of Bonnie Franklin's passing from pancreatic cancer broke Friday, her One Day At A Time co-star Valerie Bertinelli reacted with a touching memorial on her website
Bertinelli remarked on how Franklin 'taught me how to navigate this business and life itself with grace and humor' and finished with, 'I will miss her terribly.'
The pretty brunette felt 'blessed' to have reunited with her onscreen mother during the second season of the CBS sitcom, Hot in Cleveland.
RIP Bonnie: The two-time Golden Globe winner paid tribute to the fallen star, writing, 'Bonnie has always been one of the most important women in my life and was a second mother to me.'
In Bertinelli's 2008 memoir Losing It, she noted that Franklin, just 31 when the show began, wasn't actually old enough to be her real mother.
Even so, wrote Valerie, 'within a few days I recognized her immense talent and felt privileged to work with her...She was like a hip, younger complement to my real mom.'
Single matriarch: Franklin broke new ground with her character in the sitcom, about a young divorced mother seeking independence from her suffocating marriage
Lasting impression: During the first seven of its nine seasons on the air, the CBS sitcom was a Top 20 hit
'Remembering my friend. Rest in peace. Bonnie Franklin,' she wrote along with a recent snap of the co-stars.
Other celebrities to pay tribute to the fallen star on Twitter were Patty Duke, Dana Delaney, and Marg Helgenberger.
'Remembering my friend': Bonnie's other onscreen daughter, played by Mackenzie Phillips, also took to her Twitter to share her condolences
Helgenberger added, 'Sorry to hear about Bonnie Franklin's passing. She directed me many years ago for an episode of Patty Duke's sitcom, Karen's Song.'
Delaney wrote: 'Very sad to hear of Bonnie Franklin's death. I 1st saw her in 1970 in APPLAUSE on Bway. Please support @PanCan. Too many die too young.'
'I felt like I was 15 again': Bertinelli felt 'blessed' to have reunited with her onscreen mother during the second season of the CBS sitcom, Hot in Cleveland
While gossip blogger Perez Hilton let his emoticon speak for him, ':-('
Bonnie's family had announced she was diagnosed with cancer in September.
Screen legend: Veteran stage and TV actress Bonnie Franklin, pictured in 2012, passed away Friday due to complications from pancreatic cancer, said her family
A decade later, she was appearing on such episodic programs as Mr. Novak, Gidget, and The Man From U.N.C.L.E.
On stage, Franklin was in the original Broadway production of Applause, for which she received a 1970 Tony Award nomination, and other plays including Dames At Sea and A Thousand Clowns.
Franklin's recent credits include appearances on The Young And The Restless and the TV Land comedy Hot in Cleveland, which again reunited her with Bertinelli, one of that show's regulars.
A private memorial will be held next week, her family said.
'Very sad to hear': Other celebrities to pay tribute to the fallen star on Twitter were Patty Duke, Dana Delaney, and Marg Helgenberger