Can my husband gain custody of his child who is placed in temporary guardianship?

I am reiterating these statement basing on my husband's story. The first and last time my husband saw his child was the day his daughter was born, almost 5 years ago. During that time, my husband and his ex-girlfriend have a troublesome relationship, on-top of being a guy lost in translation (foster child, no guidance, kicked out from a home after he turned 18, so on and so forth). At that time, my husband was supporting his ex-girlfriend (granted no proofs of funding) because she never worked on the entirety of the relationship, yet, she was always high on something. The following day, when my husband went to visit his child, he was denied. I found out later on that his ex-girlfriend accused him of breaking her pinky finger. Because my husband at that time had legal troubles, he was taken in for questioning. And because he was found guilty on the legal trouble, the ex-girlfriend's accusations piggy-backed, though he never pleaded guilty on the accusation of violence. Though my husband was incarcerated at that time he was able to send an objection. My husband served his time and got out of parole, free and clear of any problems from the past. We have also moved out, in-search of a better and quiet life. Now, my husband has become an upstanding citizen, a homeowner, a good provider, a loving step-father who loves his family very much. A man loved by neighbors and friends, and specially by his family. Just recently, his ex-girlfriend found him on social media and sent him a message, informing him that the temporary guardians of their daughter is now filing for adoption. What are my husband's chances of acquiring custody against the temporary guardians? What steps must he do? What are the best ways to tackle this?