"Thy brother was popular, to have two sworn brothers. No wonder he was counted among the cultivation world's eligible bachelors." A tease, but a softly-made one. From the way Lan Wangji has described him, Claudius imagines Lan Xichen as a kind, attentive man who cares as deeply as Lan Wangji himself does, and who would've taken his oaths of brotherhood seriously. A loyal man, whose heart would be divided between two of his sworn brothers' enmity for each other -- and Lan Xichen lost them both. It's sincere, when Claudius says, "It's a shame his heart was not treated more kindly."