The Die Hard actor's family revealed earlier this year he'd been diagnosed with a rare form of dementia.
Demi Moore and Bruce Willis welcomed their first grandchild back in April.
"Seeing my father hold my daughter today was something I will treasure for the rest of my life," Rumer wrote on Instagram.
The A-list exes' daughter Rumer Willis has announced the arrival of her baby girl.
"My birthday wish for Bruce is that you continue to keep him in your prayers," the Die Hard star's wife Emma Heming wrote on Instagram.