This paper reports the collecting of adult beetles and third-instar larvae of Coelocorynus desfontainei Antoine, 1999 in Cameroon and provides new data on the biology of this high-altitude Afromontane genus. It also presents the first diagnosis of this genus based on larval characters and examination of its systematic position in a phylogenetic context using 78 parsimony informative larval and adult characters. Based on the results of our analysis we (1) support the hypothesis that the tribe Trichiini is paraphyletic with respect to both Valgini and the rest of the Cetoniinae, and (2) propose that the Trichiini subtribe Cryptodontina, represented by Coelocorynus, is a sister group of the Valgini: Valgina, represented by Valgus. The larvae-only analyses were about twofold better than the adults-only analyses in providing a phylogenetic resolution consistent with the larvae + adults analyses. Only one of the ten clades was consistently supported by the analyses of both the larval and adult datasets, while the remaining nine were invariably strongly supported by one but not the other analysis, thus highlighting the importance of employing different data sources.