Older sister of the late web video star Talia Castellano, popular for her beauty and fashion YouTube channel TaliaJoy18.
Her younger sister was diagnosed with neuroblastoma, a rare childhood cancer.
Mattia is very involved with the children's cancer foundation Talia's Legacy. Her Instagram handle is mattia_joyce.
She grew up in Orlando, Florida. Her mother is Desiree Castellano.
Her sister appeared on the Ellen DeGeneres show in 2012.