I think Chloe is going to come down with some kind of illness (that’s why she’s come back) and it turns out that she needs a transplant of some sort....
Ange is tested and isn’t a match...
Ange is told that it’s very unlikely a donor will be found if there’s no other family/DNA option and meanwhile Chloe is getting sicker and sicker...
Therefore Ange decides that Chloe should know about Dom because he’s her only possible chance at life.
So it all comes out, Dom is the hero and saves Chloe’s life by donating a kidney or bone marrow or something and they all become one big happy family.