Your ex-spouse could inherit your money. How to avoid this and other estate-planning mistakes

One such shocker was a plot twist in HBO's new revival of "Sex and the City," titled "And Just Like That."

(Caution: Spoilers ahead.)

The show's main character, Carrie Bradshaw, finds out upon the reading of her deceased husband's will that he has left $1 million to his ex-wife.

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"When people have unfinished business, they tend to throw money at it," a lawyer on the show states.

"Why is she in there at all?" Bradshaw, played by actress Sarah Jessica Parker, later asks.

A made-for-TV scenario where an ex's name shows up in a will hardly reflects typical real-life circumstances, according to New York estate planning attorney Martin M. Shenkman.

"In 40 years, I have never seen anybody leave their ex-spouse anything," Shenkman said.

However, there are exceptions where you could inadvertently leave money to people you no longer intend to, much to the surprise of other heirs.

The only exception where an ex-spouse could perhaps be on the receiving end of your money when you die is if you neglect to change your beneficiaries under a retirement plan, Shenkman said.

State laws generally make it so that once a married couple is divorced, ex-spouses lose all property rights.

But because pensions are governed by federal law, formally known as ERISA or the Employee Retirement Income Security Act of 1974, state rules don't apply.

So if you fail to update your beneficiary designations, your ex could still stand to inherit the money.

Pensions are not the only accounts that people tend to forget to update. Bank account beneficiary designations are often difficult to find, and circumstances tend to change from when you first set them up, Shenkman said.

In a recent meeting, Shenkman discovered a wealthy couple had nine bank accounts, excluding their brokerage accounts, at six different financial institutions. His advice to them was to whittle that down to two, preferably at the same bank to make managing them — and the respective beneficiary designations — easier.

"Simplify," Shenkman said. "Consolidate. Get a handle on what you have."

While it may be tempting to disinherit someone you have fallen out with, Shenkman said he generally tells clients not to take that approach.

"It's mean-spirited and it can invite all sorts of problems like a will challenge," he said.

There is always the chance you may reconcile, even on your death bed, at which point it will be too late to update your will and estate plan, Shenkman said he typically tells clients.

"Leave something less to them," he said. "Don't say anything nasty.

"Be hopeful that you will reconcile."

However, as the modern concept of what comprises a family continues to evolve, some people may decide to also include friends who feel like family in their wills.

Those instances, known formally as unnatural bequests due to the fact that they do not include typical beneficiaries such as a spouse and children, should be shored up with specific language to make it known it was not an accident, Shenkman said.

An example could be: "I leave my friend Jane $1 million even though that reduces my bequests to my children, because of the wonderful and supportive friendship I have had with Jane for more than three decades."

To ensure your wishes are carried out the way you want them to be, enlisting the right professional is key, whether that be a lawyer, accountant or wealth advisor.

"The most important thing that the independent professional brings is objectivity," Shenkman said. "It's really hard to see the mess you've created yourself."