9:00pm PT — Law enforcement sources tell TMZ Fiona died at home Tuesday. Our sources say authorities were called to the home at 12:10 am.

Rob Lowe’s brother, Chad Lowe and his wife, Kim Painter, are mourning the devastating loss of their teenage daughter … Fiona who died at 13 years old.

The family tells TMZ in a statement, “We are deeply heartbroken by the loss of our beloved Fiona.”

Chad and Kim remembered their daughter as a loving, smart and creative young girl who loved to dance, saying she was adored by her sisters and deeply loved by her parents.

The family added Fiona was “the light of our lives,” calling her death devastating for their entire family and asking for prayers and privacy as they grieve.

Fiona was born in November 2012 and was one of Chad and Kim’s three daughters.

The tragedy comes after an already incredibly difficult period for the Lowe family. Chad revealed last year their home was destroyed in the Pacific Palisades fire. He later shared Fiona and her sisters returning to see what remained of the home where they grew up.

Chad — the younger brother of Rob Lowe — and Kim have been married since 2010.

Fiona was 13.

RIP.