Gigi and Bella Hadid's recently discovered half-sister, Aydan Nix, is opening up about her growing bond with the supermodels. Gigi, 30, and Bella, 29, announced in May that they have a 23-year-old half-sister, born of a brief relationship their father, Mohamed Hadid, had over 20 years ago with Terri Hatfield Dull. In addition to Aydan, Mohamed shares Gigi, Bella and son Anwar, 26, with ex-wife Yolanda Hadid. He also has two daughters - Marielle, 45, and Alana, 40 - with first wife Mary Butler.