0 used to emphasize something that you are telling someone:
She's a very nice person, I'll have you know.
I may look young, but I'll have you know I'm old enough to be your mother.
And - as she'll have you know - it's an important job.
NOVÉ SLOVÁ
European
May 10, 2021
SLOVO DŇA
Shimmer
I'll, he'll, etc. have you know