Filiti was diagnosed with lung cancer earlier this year and was reported to be recuperating at the home of Sylvester's mother Jackie Stallone.
Jackie has now confirmed to the New York Daily News that the cancer spread to Toni Ann's brain and ultimately took her life on Sunday (August 26).
"I was holding her in my arms. I had just washed [her] face and told her how pretty she looked, and she just fell asleep," Jackie recalled.
Jackie went on to express her grief that Filiti died not long after the tragic passing of Sylvester's son Sage Stallone at age 36.
"She's too young to go, but she wasn't feeling any pain. What a terrible month. First Sage and now Toni," Jackie said. "It's hard. At least they're together now in heaven."
Sylvester spoke out publicly after his son Sage's death in July, asking the media to grant his family privacy.
"This agonising loss will be felt for the rest of our lives. Sage was our first child and the centre of our universe and I am humbly begging for all to have my son's memory in full left in peace," he said.