弟さん（おとうとさん）— younger brother (someone else’s)
友達 の 弟さん は 学生 です。
My friend’s younger brother is a student.
弟さんおとうとさん
younger brother (someone else’s)
おとうとさん
accent [4]In detail
Words
友達tomodachifriend
のno(possession: ’s)
弟さんotōtosanyounger brother
はwa(topic marker)
学生gakuseistudent
ですdesu(polite sentence ending)
Kanji
弟テイ・
弟さん is a polite way to refer to someone else’s younger brother. When speaking about your own, use 弟 without さん.
Coco-sensei