Relying on a decades-old inheritance law, the state’s highest has court ruled that spouses are entitled to one-third of their deceased spouse’s estate — when they are not mentioned in the spouse’s will.
The Supreme Judicial Court ruled unanimously on Monday for the second wife of a Charlton man who demanded her share of the real estate her husband had willed his four adult children. The court ruling relied on legal principles dating to 1783 that were most recently updated in 1964.
In the ruling written by Justice Elspeth B. Cypher, the court concluded that widow Susan Ciani was protected by the law as it is currently written and has the right to effectively cancel out the estate plan her husband approved before his death.
In the most recent version of the law, it is clear that “the Legislature intended for the surviving spouse to have an ownership interest in the real property for life, not merely an interest in the income produced by the real property,” Cypher wrote.
According to the SJC, Raymond Ciani made out a will in 2000 that left his estate to his first wife, Mary. Under the will, after her death, his four children were to be sole beneficiaries of the estate, which was worth an estimated $675,000. Mary died before her husband.
Raymond married Susan in 2013 and died in 2015 without having changed the original will, according to court records.
After her husband’s death, Susan Ciani challenged the will in court and remained in what had been the family home, according to court records. Both sides went into Probate and Family Court and have since agreed to sell the family home and other assets while judges decide who gets what.
Susan Ciani’s attorney, Katherine A. Bagdis, said Monday the legal battle has been an emotional drain for her client and said she was pleased that the ruling benefits her.
Bagdis said that Raymond Ciani never took an affirmative step to keep Susan out of his estate, which he could have done, for example, by putting the real estate into trusts. But since he didn’t — and he is not around to say whether it was deliberate or an oversight — the law protects spouses like Susan Ciani.
“How could anybody say what this person wanted?’’ Bagdis said. “How could they know it wasn’t his intention for his spouse to get something?”
The attorney for the four children, Maria L. Remillard, said the SJC has created what could become a legal morass for blended families, because the law is obscure, even to lawyers.
“It’s a rude awakening for a lot of people,’’ Remillard said of the law and the SJC’s endorsement of it. “It isn’t until someone passes away that the parties and surviving spouses realize the impact . . . After a second marriage, the second spouse could, in fact, totally disrupt the estate plan.”
Remillard said the SJC decision authorizes Susan Ciani to collect one-third of the value of her husband’s real estate holdings and a similar share in the estate.
If both sides had not agreed to sell the family home, Susan Ciani also would have been allowed to live there for the rest of her life, Remillard said.
At the same time, the SJC said the four children have an equal right to the family home as well — meaning that, in theory, all five people could demand to be in the house at the same time, Remillard said.
In a footnote, the SJC urged the Legislature to consider revising the law.
“As practical matter, [the law] is unwieldy and perplexing to apply in most instances,” Cypher wrote. “The statute is in desperate need of an update and we urge the Legislature to do so.”
One specialist in estate law planning agreed the law needs an overhaul.
“It has language that is impossible to understand,” said Ray Madoff, a professor at Boston College Law School.
Some states follow community property laws that allow a spouse to retain half ownership of all property earned during a marriage, she said.
But Massachusetts is among the states that follow an elective share law to protect spouses against disinheritance.
Other lawyers said the court’s ruling likely will not have broad impact on estate planning in Massachusetts.
Amanda Mulhall an attorney at The Parents Estate Planning Law Firm PC in Acton, said the decision would have little effect “other than to stress the importance of keeping your plan up to date.”
“Most planners would avoid this provision and ensure there are other arrangements made,” said Sheila Giglio of the Boston firm Conn Kavanaugh.
Danny McDonald of the Globe Staff contributed to this story. John Ellement can be reached at email@example.com.