What is XXX's brothers name?
Christiaan Huygens
Christiaan Huygens, FRS (/ˈhaɪɡənz/ or /ˈhɔɪɡənz/; Dutch: (ˈɦœy̆ɣə(n)s)) (Latin: Hugenius) (14 April 1629 -- 8 July 1695) was a prominent Dutch mathematician and scientist.