AAS,
Again, I am so sorry and furious for you.
Once again, our sagas intersect: my STBXWW became pregnant with POS's child around a year ago, ld me to believe it was mine, aborted and then told me she did it as a sacrifice and love for me. Sick.
Recently my DD told me "Mommy is going to have another baby."
I can't offer anything on the legal aspects that others have posted, and all I can do is reiterate what others are commenting in other respects:
First, to state the obvious: this is final (maybe) proof just how distorted your CSTBXWW is. If ever--EVER--you still wondered if she would come to her senses and return, I am sure these thoughts are now banished. They'd better be.
What this will do to your kids can only be traumatic. 99% of her attention WILL be on this child (if she carries to term). And the kids will quickly experience this and it will do damage. Thank god for your presence. When this child is born, she will be "gone."
And so likely will their relationship, if this gives you any small degree of solace and sense of justice.
All of us with kids know how profoundly life-changing a newborn is. I was thirty six when we had our first, and I can tell you, I was in shock--and not in a good way--for a good two years.
Like Gru, I had led a single life and then within two years I had a baby and wife. This created unbelievable strain on our relationship at the time and I remember, in the throes of sleep deprivation and desperation, seriously contemplating leaving her.
And our union was forged in real love--not in deceit, betrayal, cruely and lies. Gru is in for an incredible shock. They will continue to desperately "bond" through the new child, but it will prove to be a grenade in their relationship.
But to return to your children: they will suffer at least to some degree; this is assured. Please speak with your solicitor ASAP and see if this can merit filing for at least majority custody.
I know you say you are not surprised and not as upset as you thought you would be, but as another poster indicated, you may very well have a delayed reaction, for as "predictable" though this may be, it is still a shocking blow.
Be easy on yourself, and let your anger direct itself to renewed protection of your kids who should not be with their so-called mother. She is out-of-control. This is intolerable and changes the "game," hopefully in your favor. They must be with you, AAS. I hope she has just hung herself.
What a terrible person.