suffix
honorific suffix for someone else's family member
Attached to a family term to refer politely to the listener's or a third person's family member. Not used for one's own family.
お父君はお元気ですか。
How is your father?
ご母君によろしくお伝えください。
Please give my regards to your mother.
さん is a general polite suffix for people, while 君 (ぎみ) is specifically an honorific suffix attached to family terms when referring to someone else's family.
The kanji 君 (kun/kimi) is used as an honorific suffix for family members, read as ぎみ. The exact derivation of this reading is uncertain.