You could sue him in civil court but it would be easier to just have the court grant you relief. You can ask for equitable relief and other sanctions. You should not have waited so long as it is less likely that you will get it than if you would have acted right away.
This is not a comprehensive answer and it is impossible to provide a meaningful response without a consultation. Call us for more information. 619.797.5456 www.mataelelaw.com
Since 6 years have passed since your divorce occurred it may be too late. I suggest you consult with a local experienced divorce attorney and present all of the facts of the case so that you can get the answer to your question.
The statute of limitations for fraud is 3 years from the date of discovery of the fraud. You should consult with an attorney to determine your rights and the type of relief you can seek at this point. There's far too much information missing form your question to figure out what your next step may be (if any).
Sign up to receive a 10-part series of useful information and legal advice about the divorce process.