This! Also had this happen many moons ago with a nice girl and immediately said impossible for me to have kids, after which she said she wasn’t pregnant. Many will try to trap you. If indeed she is pregnant, suggest DNA test if and when the time comes.
In any case, just chill out a bit; if she’s as nice as you say and it is all true, divorce yourself cheating skank of a wife, take the kids and marry this one.
All the best.