He is known to everyone.
I have known him a long time.
She's well known as a singer.
Have you known her since 1990?
His face is known to many people.
She has known him for a long time.
They must have known it all along.
How long have you known Miss Smith?
The cause of the fire is not known.
You must have known what she meant.
I have known Tom since I was a little boy.
She has known him since they were very young.
Tom and Sue have known each other since 1985.
John and Mary have known each other since 1976.
She wouldn't have married him if she had known him better.
If he had known her phone number, he could have called her up.
If I had known about your illness, I could have visited you in the hospital.