The facts we know so far
1. From the looks of it seems like AD has no family of his own - adopted sisters, MIL and wife.
2. Also the level of hatred for JW means it has to be something personal. He was also lighting a Dia, so probably is in front of a person or family.
3. JW does not recognize him so the identity AD must be an assumed one and probably one that he took on 25years ago when the story started for him
4. Both are now (after the 5 year leap) about 45 years old so the incident happened when they were about 20 years old.
So these are the facts that we know so far
If the picture is a family and if it is Jai who is the culprit it must be some form of accident that Jai cuased that destroyed AD's family. Other could be UW might be responsible for some business dealings (like bankrupting his family) that made AD loose everything and now JW is the target as he is his fathers waaris. Or the fav guess on this forum of the trishul movie reference AD is the illegitimate child of UW and UW left his mother to marry the rich KW and destroyed his mother's life.
If the picture is a girl - lover or a sister. JW could have been responsible for breaking her heart and her destroying herself for it. I don't know if this sort of intense hatred could come from this scenario.
I am leaning towards somehow AD's mother being involved or his family and UW is the culprit.