Photo: Tim Tebow/Instagram

Demi-Leigh Nel-Petersandher fiancé, former football playerTim Tebow, are mourning the death of her 13-year-old half-sister Franje.
The former Miss Universe, from South Africa, shared the sad news via on herInstagramon Saturday.
Franje was born with an extremely rare condition calledcerebellar agenesis, where the brain forms without a cerebellum. The cerebellum provides motor control to the body, and helps with attention, language and coordination. Living without it can mean developmental delays and trouble with basic movement.
Franje Peters.Demi-Leigh Nel-Peters/Instagram

Nel-Peters and Tebow owe their relationship to Franje. The couple met atNight to Shine, his annual prom for kids with special needs, which benefits his Tim Tebow Foundation.Tebow invited Nel-Petersafter learning about Franje.
“We met because of Night To Shine,”he told PEOPLE following their engagement in January. “So it’s great for her to experience the things that are important to me.”
Demi-Leigh Nel-Peters and Franje Peters.Demi-Leigh Nel-Peters/Instagram

Tebow also shared a tribute to Franjeon his Instagram page on Saturday, along with a photo of all three of them.
“Our loss but heaven’s gain,” he wrote. “So grateful for the hope we have of being reunited with the ones we love through our Heavenly Father. Mr. & Mrs. Peters and@demileighnpwe are praying for you and love you so much.”
source: people.com