Adopting stepchild after divorcing the mother

Is is possible, in the state of Michigan, to adopt a stepchild after divorcing the mother of said child? Here's the situation:The child was three months old when I met his mother. The biological father was never in the picture, other than paying child support. Other than child support, there has been no contact with the biological father and the child turns 11 years old in November. The mother and I were married for three and a half years and had one child together. We have both remarried since and all parties involved get along great. I get to have the eldest child with me whenever I have the child we had together. He knows me as his father, but he also knows he has a biological father somewhere else. We had planned on me adopting the eldest child while we were married, but never got around to it before the divorce. She is now in the process of developing her Will/Estate Plan and we were made aware that even though she wishes the two children to go to me in the event of her death, that may not happen with the eldest child because there was no adoption. We would like to have a legal adoption of the eldest child by me, even though we are divorced. Is this possible?