You will definitely want to tell them about it and have in writing that they recognize that what is yours is yours. If they ask you to assign it to them politely tell them no. The worst situation you could be in is to have them find out in the future with some notion that you wronged them. If they press the issue of IP with you can decide at that point what you want to do.

For what it is worth, I joined a startup with a bogus "all your ip is now our ip" clause as well as an overly broad "non-compete" clause. I simply struck those entire sections from my contract. In the end, they asked me for a list of my IP/inventions and I provided them the folder structure of my side projects drive. I agreed (in writing) that I would never work on any of my own IP with their resources.

I told them flat out that I would accept an alternate offer if the perused the issue. I recognize that this is a different time (given the uncertainty of how the virus will affect the economy) but I feel strongly that what is yours is yours and joining a company does not give them the absolute right to anything you have done prior.