The resort where the couple were staying confirmed to NBC News that a male guest drowned while freediving alone outside the underwater room on Thursday.
An American man has died while proposing to his girlfriend underwater during a vacation in Tanzania.
Steven Weber drowned while asking Kenesha Antoine to marry him at an island resort off the east coast of Africa Thursday.
Antoine shared the news of Weber's death on her Facebook page, saying that he "never emerged from those depths."
She also posted a video of the proposal.
In it Weber can be seen holding a handwritten note in a waterproof bag up to the window of an underwater room — part of a luxurious offshore water cabin that the couple was staying in at The Manta Resort, off Pemba Island.
"I can't hold my breath long enough to tell you everything I love about you but everything I love about you I love more every day," the note read.
He then flipped the note to show the other side, which read: "Will you please be my wife. Marry me?"
Weber then produced a ring before swimming up out of view.
It's not clear from the post what happened after that. NBC News has reached out to Antoine for comment.
Antoine wrote that Weber never got to hear her answer, which would have been "a million times, yes."
"We never got to embrace and celebrate the beginning of the rest of our lives together, as the best day of our lives turned into the worst, in the cruelest twist of fate imaginable," she said.
"I will try to take solace in the fact that we enjoyed the most amazing bucket list experiences these past few days, and that we both were so happy and absolutely giddy with excitement in our final moments together."
The Manta Resort confirmed to NBC News that a male guest drowned while freediving alone outside the underwater room on Thursday.
The resort's CEO, Matthew Saus, said they were "devastated" by what happened and "still trying to recover."
"Our sincerest condolences, thoughts and prayers are with his girlfriend, families and friends impacted by this tragic accident," Saus said.
He added that a local police authority is investigating the incident.
Saus did not say anything about whether a rescue or resuscitation had been attempted or what the sea condition was at the time.
A State Department spokesperson told NBC News on Saturday that they are aware of reports of the death of a U.S. citizen in Tanzania.
"We offer our sincerest condolences to the family on their loss. We stand ready to provide all appropriate consular assistance," it said.
Weber's Facebook account states that he worked at an addictions wellness center in Baton Rouge, Louisiana, while Antoine is listed as an owner and principal attorney at a notary and legal service provider in the city.
Antoine called Weber "a bright light to everyone [he] encountered," adding that he "brought so much joy to so many people."