For the past three years, retired model and "Real Housewives of Beverly Hills" reality star Yolanda Foster has been very outspoken about battling Lyme disease, even taking singer Avril Lavigne under her wing upon hearing of her own diagnosis - but it turns out that, out of Foster's three children, two are struggling with this disease as well, including Gigi Hadid's sister, Bella.

On Thursday night, Foster accepted the Power of One award at the Global Lyme Alliance Gala in New York City accompanied by her family, including top model daughter and her boyfriend Joe Jonas, and revealed that Gigi Hadid's sister, as well as her brother Anwar, are also battling this condition.

According to TMZ, Foster spoke of how Gigi Hadid's sister and brother were diagnosed with Lyme disease in early 2012, around the same period as she was, although their condition has been kept under wraps for the past three years.

"When my two youngest children, Bella and Anwar, were diagnosed with chronic Lyme disease in early 2012, watching my babies struggle in silence in order to support me in my journey struck the deepest core of hopelessness inside of me," Foster said during the event, speaking of how huge the fight has been for the family, including Gigi Hadid's sister.

Later on, the top model and Kendall Jenner close friend also spoke about her family's struggles to Entertainment Tonight Online, tearfully revealing that it's been hard for her because she's "the only one that doesn't really understand" what the rest of her family's going through, as three of her closest people have been battling with this debilitating condition.

The 20 year-old model has also revealed that the situation has brought the whole family closer, adding that her mother, brother and Gigi Hadid's sister were her best friends.

Besides the Hadids and Lavigne, Pop Mythology reports that a handful of celebrities have revealed their struggles with Lyme disease, including Richard Gere, former President George W. Bush, Christy Turlington, Parker Posey, Ben Stiller and reportedly Olsen twin Ashley, though Elizabeth Olsen's big sister has failed to confirm these rumors.

While the news that Bella Hadid's sister and brother have been battling Lyme disease in silence for so long is heartbreaking, it's still a relief to see how much support they've found in their loving family.