Gigi and Bella Hadid are so welcoming to their secret half-sister! As we previously reported, the Hadid sisters were in for a huge shock when they found out 23-year-old Aydan Nix was their half-sister. Their dad, Mohamed Hadid, had a short lived relationship with Terri Hatfield Dull after he divorced from Yolanda Hadid, which resulted in Aydan! The Hadid patriarch always knew of his child with Terri, but the Hadid siblings didn't find out the news until Aydan took a DNA test and it matched her up with them earlier this year.