Do you have any record of him saying this? Text messages, witnesses? If so, drag his scummy ass to court.

take it up in front of the judge. he'll most likely be ordered to pay all of uni costs, or at least half.

You can contest the will, stating exactly what you just said. Just add that she "forgot" to change the will to make sure that promise was kept.

OP the way you stated it sounds a lot like the kids in question are not your ex’s children. Their father (and you) owe for their support - Not your ex unless he had adopted them… Ultimately people say a lot of things, sometimes just saying what the other person wanted to hear. A signed document however is another thing and stands up in court… OP sometimes life does not seem “fair”. But there are laws that usually prevent the most awful wrongs. It is always wise to understand where things stand legally.

Did he say this when yall were together or after? That bit of context makes all the difference in the world

You said to "your" kids. Are they his, too? If so, he's a total asshole. If not, you should have gotten it in writing.