New(er) foster parent asks: How do you handle this?

I've been a foster parent for about 4 years, but only on my 3rd kid. I have a question I hope some other more experienced foster parents can answer. My new placement has shared with me, in confidence, details about his family that I think the agency doesn't know about (being coached for court by parents, visits not taking place as they are prescribed, to name just a couple). He shared this with me only if I promised not to tell anyone. That said, these are clearly important details that the social worker would probably want to know to help manage his case. How do you handle this? I'm worried that if I share all the information with the social worker, it will almost definitely get back to the bio parent, who will then talk to the kid about it, and he will believe I violated his trust. It's to his and my benefit that he feels he can talk to me about anything and I'm glad he's comfortable in doing so. That said, it's clearly in the best interest of all involved (court, social worker, agency) to know the information so they can make good decisions based on it. This may be a very basic question but it's new territory for me. Any thoughts appreciated!