Forged signature on a car ownership

Hallo everyone.
My friend have a situation now. His wife forged his signature and sold his car to herself. So she is the owner now. It happens last summer and he discover few months ago when paying road tax in Naas. They don't live together for a while but not in divorce yet. Is it criminal matter?
Did anyone know how to act in this situation?
Lady doesn't want anything in this world more than leave him without a cent.
Can't find information on web about it. Shannon department of transport never reply on email. Can't get them on the phone too.

Yes, it's fraud, so it is a criminal matter.

it is a crime and your friend will have to make written statement of complaint to the gardai if they want any thing done

Thank you Leo and Thank you rosemartin for reply