Mabel added several photos of her childhood with her younger sister, as well as a final photo of Fiona dancing to the upload.

The Lowe family — which also includes the “Pretty Little Liars” actor’s wife, Kim Painter, and their youngest daughter, 10-year-old Nixie — announced the devastating news that Fiona died on Sept. 29.

She was 13 years old.

“We are deeply heartbroken by the loss of our beloved Fiona. She was a loving young girl who was smart, creative and loved to dance,” the family shared in a statement to Page Six.

“She was adored by her sisters and she was deeply loved by her parents. In fact, she was the light of our lives. Her passing is devastating for our entire family and we ask for prayers and privacy at this time.”

The statement concluded, “If you or someone you know is struggling with mental health, please reach out to the 988 Suicide & Crisis Lifeline by calling or texting 988.”

Mabel shared the statement on her Instagram Stories on Sept. 30, along with a pic of Fiona grinning at the camera.

Lowe’s father, Charles “Chuck” Lowe, also honored Fiona one day following the announcement of her death, sharing a photo of the teen smiling at the camera as she swam in a pool.

“Rest in peace, sweet Fiona,” he wrote in the caption.

The Lowe family has remained relatively private over the years. Fiona’s last red carpet appearance with her family was a rare public outing at the premiere of Marvel’s “Moon Girl and Devil Dinosaur” on Feb. 4, 2023, in Burbank, California.

Fiona posed in the middle of her sisters, with her dad keeping his arm around Mabel.

The “Bones” actor, 58, has shared more than once that being a dad to three daughters meant the world to him.

“It’s so interesting because always wanting to have my own experiences and not live in the shadow or follow in the footsteps of somebody, I get the experience of being a girl dad, which is such a privilege,” he said on the “Still Here Hollywood” podcast in August 2024.

In February 2024, he shared that being his kids’ dad is his life’s “greatest joy and privilege” after seeing how they dealt with their home being destroyed in the devastating Palisades fire.

“I am in awe of their spirit and resilience,” he shared on Instagram along with pics at his family looking at the remains of their home. “Helping them navigate these tough times is my sole purpose.”