So you're saying she signed a pre-nup? Even if she did, she still has to sign-off on not having interest in the 401k, it's not automatic. If he had a bank account that she wasn't on, would this go to the ex-wife? If their house was in his name only (or they had a rental property) would that go to the ex-wife? Why do you believe the ex-wife would get the entire nut rather than the portion she had already agreed upon during their divorce negotiations? When you die, your current assets go to your spouse unless you have made very specific prior legal arrangements. They don't go to an ex, even if that ex already owns a part. A good example, I had a relative recently pass and had explicitly willed all of his belongings to his children. His ex was still listed as part owner on their rental properties (they continued to run that as a business after they divorced). She did not suddenly own all of those properties outright, his children now own his half. If he had remarried and had no will, I expect his new wife would own his half.