Developer Mircea Voskerician says Zuckerberg broke his word. Zuckerberg's lawyers say that's nonsense, and that Voskerician is trying to squeeze money out of a billionaire.
The facts, in a nutshell, are these: In November 2012, Voskerician was in a contract to buy the property behind Zuckerberg's home in Palo Alto, California. He sent a letter to the Facebook chief executive officer saying he planned to tear down the home and build an 892sq m replacement. It would overlook the back of the Zuckerberg abode, a view that would include the master bedroom.
Then Voskerician made an unusual offer. Calling himself a "good neighbour", he proposed to sell Zuckerberg a slice of the property at "100 per cent premium" to give him more privacy.
Within two weeks, they agreed that Zuckerberg would buy the entire property at what Voskerician considered a steep discount.
Why would Voskerician do that? This is where the two sides disagree. Voskerician, in court filings, says Zuckerberg promised to introduce him to contacts in Silicon Valley, a valuable endorsement for anyone. Nothing was put in writing.
Zuckerberg's lawyers deny that, and all of Voskerician's claims. Whatever the case, the developer sued and unless the two sides reach a deal the case will go to trial. If Voskerician wins, he might get the property back.
The emails that have emerged during litigation offer a glimpse into Zuckerberg's private universe. And it's clear from the start that his inner circle was livid about their boss's enterprising neighbour.
In one email, a financial adviser to Zuckerberg, Divesh Makan, called Voskerician's offer an "obscene proposal". In another, Zuckerberg's then-personal assistant, Anikka Fragodt, wrote, "This type of behaviour makes me want to punch people in the face."
Zuckerberg's wife, Priscilla Chan, lamented, "It's stuff like this that makes me so sad and angry." She asked whether Makan could quietly figure out if the couple could buy Voskerician's entire section.
Zuckerberg's lawyers, in court filings, say the developer employed "extortive" tactics. They cited a November 28, 2012 email that Voskerician sent to his real estate agent in which he suggested the Facebook chief had a chance to buy some privacy.
If "Mark plans to live there long term", Voskerician wrote, he has "one shot to ensure his privacy is where it needs to be".
He goes on to say the new home would be built "overlooking his backyard/master bedroom". Emails from Voskerician show how much he wanted to gain entry to the rarefied realms of Zuckerberg's world.
In an April 13, 2013 email to Zuckerberg, Voskerician asked to "shake hands" on the deal and begin the introductions.
"Mr Zuckerberg, First I am happy that I could maintain your privacy by selling you the Hamilton property," the Romanian-born Voskerician wrote.
"Second, I wanted to meet and shake hands for the transaction and discuss your offering of working with you in the future as you stated you have built Facebook on connections that you have with others in Silicon Valley.
One of the reasons I went with your offer other than maintaining your privacy was your offering to help me get my homes, development projects, in front of your Facebook employees and build a relationship with you."
Voskerician also asked for a 30-minute meeting with Zuckerberg to discuss a project involving "modern science-based sustainable social living" using an an "open source" model akin to Facebook's "Open Compute Platform". Emails suggest the Zuckerberg team had zero interest.
Makan told Zuckerberg's real estate agent the Facebook chief was unlikely to meet Voskerician at all.
"But if it means I have to waste 30 min on MZ's behalf I would grudgingly do it if you advised this," he wrote in an April 2013 email.
Voskerician kept nudging, to no avail. By November 2013, Facebook employees were starting to worry he could cause problems.
Zuckerberg's assistant, Andrea Besmehn, briefed the company's head of executive protection in case the standoff "escalates from either a security or PR standpoint".
Besmehn sent an email later that day on which the case could now turn: "I just had a quick chat with Mark on this issue - and he said he does remember saying that he would help this guy in a 'light' way," Besmehn wrote to Makan and others.
"Is there a way when we chat with him that we can find out a way for us (not necessarily Mark) to help him with something small? Also ... we'll have to manage this carefully because we don't want to give an inch ..."
Voskerician's lawyer, David Draper, declined to comment on the complaint, which includes allegations of fraud, breach of contract and misrepresentation. Zuckerberg denied all the allegations in an October court filing.
While verbal promises can be difficult to pin down, Voskerician's claim that he had an agreement stands a good chance of being used as evidence, said Saint Louis University law school professor Miriam Cherry.
The email from Zuckerberg's assistant saying he recalled agreeing to help Voskerician in a "light way", while not a first-hand account, "is still convincing as to what his state of mind was", Cherry said.
California had a "loose standard" of letting such understandings be used as evidence.
A law professor at the University of California at Irvine, David Min, said the case could come down to whether Voskerician can prove Zuckerberg made a real promise.
"Oftentimes these can come down to a he-said, she-said face-off," Min said.
However the case turns out, Zuckerberg's privacy is unlikely to be threatened by other neighbours thanks to Makan, the former Goldman Sachs Group and Morgan Stanley executive who described his team as "Mark's family office".
As Voskerician pressed his demands more insistently, Makan's firm, Iconiq Capital, bought other properties surrounding Zuckerberg's home, buying one for US$10.5 million ($14.14 million), another for US$14 million and a third for US$14.5 million, according to the Santa Clara County tax assessor's office. Those prices eclipsed the assessed value of the properties, which in 2013 were less than US$3.5 million. Bloomberg