noun, adverb
since we last met; since parting
A formal, somewhat literary expression used in letters or formal speech to refer to the time since one last saw someone. Often used at the beginning of a letter.
一別以来、お元気でいらっしゃいますか。
I hope you have been well since we last met.
一別以来、十年の歳月が
Ten years have passed since we parted.