Jennifer Aniston "broke down uncontrollably" at her mother's bedside after she had a stroke.
The former 'Friends' actress - who was estranged from her mum for 12 years after she gave an interview about their relationship in 1996 - visited 75-year-old Nancy Dow in hospital over the weekend after she suffered the brain seizure and was overcome with emotion as soon as she saw her.
A source told the Daily Mirror newspaper: "Jen headed for the Los Angeles hospital the second she heard - Nancy is desperately ill, and it is no exaggeration to say people fear the very worst.
"She's distraught - it was made more difficult because Nancy can't really speak at the moment. There is plenty they'd like to talk about."
Jennifer - who was accompanied to the hospital by boyfriend Justin Theroux - and her mother publicly fell out after Nancy went on TV and spoke about the 42-year-old star.
However, Jennifer previously confirmed she and her mother - who was not invited to her wedding to Brad Pitt in 2000 - were back on speaking terms after ending the rift in 2008.
She said: "It's good. It's OK. Things are now fine between us. All of that is over, and we're in touch with one another. We speak and it's all over."
Nancy - who had Jennifer with actor John Aniston - has previously written a book about their life, entitled 'From Mother and Daughter to Friends'.