In short, Kylo meeting his child for the first time and Hux raising the kid and escaping from the catch of Resistence.
Kylo Ren has returned to the light side and Hux(with Milicent please?) has disappeared completely without a trace. A few years later, when Ben Solo(who's still under survillence because of his sins) went to a very remote planet on a mission and surprisingly met Hux with a son or daugter(or both),who resemble(s) the face of Ben and Hux. Hux kept the news from Kylo back then probably because afraid that Kylo and Snoke would not agree to. But then the First Order was defeated so he escaped and raised the kid alone. It's definitely not easy for a fugitive of a galaxy to raise a kid when you have nearly nothing left. Ben should already realize that through the force but he had declined the dark power for too long.
Kylo Ren/Hux (Alpha!Ren/Omega!Hux) Kylo meeting his child for the first time
Kylo Ren has returned to the light side and Hux(with Milicent please?) has disappeared completely without a trace. A few years later, when Ben Solo(who's still under survillence because of his sins) went to a very remote planet on a mission and surprisingly met Hux with a son or daugter(or both),who resemble(s) the face of Ben and Hux. Hux kept the news from Kylo back then probably because afraid that Kylo and Snoke would not agree to. But then the First Order was defeated so he escaped and raised the kid alone. It's definitely not easy for a fugitive of a galaxy to raise a kid when you have nearly nothing left. Ben should already realize that through the force but he had declined the dark power for too long.
The ending is up to the author.