ive ▁child hood , ▁Prince ▁John , ▁was ▁sick ly ▁and ▁died ▁young ▁( of ▁ju ven ile ▁di ab etes ), ▁eigh teen ▁days ▁before ▁his ▁wife ▁gave ▁birth ▁to ▁Prince ▁Sebastian ▁on ▁ 2 0 ▁January ▁ 1 5 5 4 . ▁When ▁John ▁III ▁died ▁of ▁ap ople xy ▁in ▁ 1 5 5 7 , ▁his ▁only ▁he ir ▁was ▁his ▁three - year - old ▁grand son , ▁Sebastian . ▁John ▁III ' s ▁body ▁rest s ▁in ▁the ▁Mon aster y ▁of ▁Jer ón imos ▁in ▁Lis bon . ▁ ▁Style ▁ ▁Like ▁his ▁prede cess ors ▁John ▁III ▁used ▁the ▁style ▁" El - rei " ▁( the ▁king ) ▁followed ▁by ▁" Dom " ▁( ab bre vi ated ▁to ▁D .), ▁a ▁mark ▁of ▁high ▁este em ▁for ▁a ▁distinguished ▁Christian ▁no blem an . ▁ ▁The ▁official ▁style ▁was ▁the ▁same ▁used ▁by ▁his ▁father ▁Manuel ▁I : ▁" Dom ▁João , ▁by ▁the ▁grace ▁of ▁God , ▁King ▁of ▁Portugal , ▁of ▁the ▁Al gar ves , ▁of ▁either ▁side ▁of ▁the ▁sea ▁in ▁Africa , ▁Lord ▁of ▁Guinea , ▁& ▁of ▁the ▁Con quest , ▁Navigation , ▁& ▁Com merce ▁of ▁Eth iop ia , ▁Arab ia , ▁Pers ia , ▁& ▁India " ▁( Dom ▁João , ▁por ▁gra ça ▁de ▁De us , ▁Re i ▁de ▁Portugal , ▁e ▁dos ▁Al gar ves , ▁d ' aqu ém ▁e ▁d ' al ém ▁mar ▁em ▁Á frica , ▁Sen