Jennifer Aniston's mother, Nancy Dow, has suffered a serious stroke.

The actress, 42, visited her ailing mother, 75, at an L.A.-area hospital on Friday. At her side for the ordeal was live-in boyfriend, Justin Theroux.

"Justin has been very supportive and there with her all the way," a source tells Us, adding that clearly, "It's a very hard time for her right now."

Aniston's rep said only that "this is a private family matter."

Fans of the star may recall that she and Dow were estranged for a decade after Dow spoke out about their relationship in a 1996 interview and wrote about Aniston in a book, From Mother and Daughter to Friends: A Memoir.

They have since reconciled. Here's wishing both the best ...

[Photo: WENN.com]