The actor, 68, is battling frontotemporal dementia, which can create issues with language comprehension and communication. His wife Emma Heming Willis has been spreading awareness about how the disease can affect one's body and mind.
Rumer, 35, his eldest daughter with ex-wife Demi Moore, shared a throwback photo of herself as a baby in her dad's doting arms, and penned alongside it: "Really missing my papa today."
The actress received heaps of support from fans, who encouraged her to remain strong with responses like: "Hugs. It's an odd kind of hard to miss someone who is still here. Dementia is a cruel beast."
A second added: "The love between father and daughter transcends physical distance, for the bond we share is stronger than any space we are separated from!" with a third offering: "My heart hurts so bad for you & your family. You have so many who are praying, including myself."
Through his health issues, Bruce has received the unwavering support of not only Emma and their two daughters, Mabel, 11, and Evelyn, nine, but also ex-wife Demi and their three daughters, Rumer, Tallulah, 29, and Scout, 32.
After announcing in Spring 2022 that Bruce was suffering from Aphasia, they shared a joint statement this February revealing that his condition had progressed to frontotemporal dementia.
The Mayo Clinic describes the affliction as primarily affecting "the frontal and temporal lobes of the brain. These areas of the brain are generally associated with personality, behavior, and language."
Rumer has since then seen her family expand, however, with the birth of her daughter Louetta Isley Thomas Willis in April, shared with boyfriend Derek Richard Thomas.
She paid tribute to both Derek and Bruce this Father's Day with a sweet photo of grandpa Bruce holding her baby girl, his first grandchild, in his arms.
"Fathers to the old and new," Rumer penned. "Seeing my father hold my daughter…was something I will treasure for the rest of my life. His sweetness and love for her was so pure and beautiful.
"Papa I'm so lucky to have you and so is Lou. Thank you for being the silliest, most loving, coolest Daddio a girl could ask for. Best Girl Dad in the game…."
As a tribute to Derek, a musician, she wrote: "Happy 1st Father's Day! Thank you for building a beautiful garden for Lou to play in and eat from. Thank you for filling the house with music for her to hear."
She continued: "Thank you for all the late night diaper changes and silly faces. I'm so grateful our girl has a papa that loves her so much and someone so goofy and weird so she knows that's ok for her to be too. Thank you for the greatest girl I could imagine in my wildest dreams. We love you."
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