Jonathan Boies, a son of renowned trial lawyer David Boies and one of the first hires at the law firm that became Boies Schiller Flexner, died on Feb. 22 of complications related to a vascular brain condition.

A source close to the firm and David Boies confirmed the death, saying it came unexpectedly in Aventura, Florida while Jonathan Boies was in the state for a family birthday celebration. The cause was a rare condition called arteriovenous malformation, which impacts blood vessels that connect to arteries and veins in the brain.

Boies would have turned 51 later this month.

Another of David Boies' adult children, Caryl Boies, died in 2010 at the age of 48, following a years-long battle with lung cancer. At the time of her death, Caryl Boies was a litigation partner at Boies Schiller Flexner. She had previously founded the firm's Fort Lauderdale, Florida, office. Caryl Boies was one of two children from David Boies' first marriage, which ended in divorce.

Jonathan, a graduate of the University of Redlands in California and Tulane Law School, and one of two children David Boies had with his second wife, Judith Boies, was the first associate David Boies hired after he split from Cravath, Swaine & Moore in the late 1990s.

In a 2017 interview, David Boies recounted how his son was set to join Kaye Scholer after graduating law school, but ultimately ended up working alongside his father.

“Jonathan was scheduled to join Kaye Scholer, but when David called his good friend and Kaye Scholer partner Jonathan Schiller and said 'I need my son,' Schiller understood,” Boies told legal blog Above The Law. (Jonathan Schiller went on to leave Kaye Scholer to become a name partner at Boies Schiller.)

By the early 2000s, Jonathan Boies had left his father's firm to pursue business ventures as an entrepreneur, and had stopped practicing law. But he remained part of the extended Boies Schiller family, said Nicholas Gravante Jr., a partner in New York and a member of Boies Schiller's executive committee.

Among Boies' business ventures was a document processing and management company he founded called SiteLogic Technologies LLC, which he eventually sold in 2015. In the years since, he was involved in an organic farming business known as Diamond B Farms and a family-owned vineyard in Lake County, California, which uses organic methods to produce wine.

Gravante, who joined Boies Schiller in 2000, maintained a longstanding friendship with Jonathan Boies. He said that even after Jonathan left the firm, the two of them typically teamed up at a tennis tournament held during the firm's annual retreat.

Gravante described Boies as fun-loving and a big sports fan, especially of the New York Jets. He also said Boies was a devoted father to his 13-year-old son, Joshua, and that the men's children were often a focus of conversation when Gravante and Boies spent time together.

“He truly loved his son,” said Gravante.

Gravante said that the firm had made a brief internal announcement about Boies' death.

“What was described within the firm was that our chairman and founder, David Boies, lost a son. It was tragic, David was devastated,” said Gravante. “Nobody loves the law more than David and no one is more dedicated to his family than David.”

From its earliest days, Boies Schiller Flexner has been somewhat of a family affair. For instance, managing partner Jonathan Schiller has a son, Joshua, who is now a litigation partner at the firm. Meanwhile, several members of the Boies family have come through the firm at different points. That includes Jonathan Boies and his fraternal twin brother, Christopher Boies, who formerly headed Boies Schiller's corporate practice. Alexander Boies, one of David Boies' children with his third wife, Mary Boies, is currently a Boies Schiller associate.

Jonathan Boies is survived by his father, David Boies; his mother Judith Boies and her husband Robert Christman; his teenage son, Joshua; his ex-wife Jodie Boies; his twin brother Christopher Boies; brothers David Boies III and Alexander Boies; and sister Mary Regency Boies.

A burial and small, private service for close friends and family are scheduled for Sunday, March 3 in New York's Westchester County, where Jonathan Boies lived.