adverb
after a long time; for the first time in a while
Used when something happens again after a long interval. Often carries a nuance of pleasant surprise or nostalgia.
久しぶりに友達に会った。
I met a friend for the first time in a while.
久しぶりに映画を見に行った。
I went to see a movie after a long time.
The noun/adjectival form used in greetings like お久しぶりです (It's been a long time). 久しぶりに is the adverbial form.
From 久しい (old, long-lasting) + ぶり (after an interval) + adverbial particle に.