Of or relating to one's alter ego; characterized by alter-egoism.
alter-egoistic/ˌɔːltə(r)iːɡəʊˈɪstɪk/ /ˌɒltə(r)iːɡəʊˈɪstɪk/ /ˌaltə(r)iːɡəʊˈɪstɪk/
Late 19th century; earliest use found in George Meredith (1828–1909), novelist and poet. From alter ego + -istic, after egoistic.
Are You Learning English? Here Are Our Top English Tips