British-Israeli hostage Nadav Popplewell was among four people who died while in Hamas captivity, the Israeli military has said.
The 51-year-old’s body remains in Gaza, it is understood.
He was taken hostage along with his mother from their home in Nirim during the 7 October Hamas attack.
On Monday, Israel confirmed the deaths of the four hostages, including three elderly men seen in a Hamas video begging for their release.
The three, Amiram Cooper, Yoram Metzger and Haim Peri, were all aged 80 or older.
The four men were kidnapped and taken into Gaza still alive, according to the Hostages Forum, a grassroots group representing the families of the hostages.
“It is time to end this cycle of sacrifice and neglect,” the group wrote in a statement following the announcement.
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“Their murder in captivity is a mark of disgrace and a sad reflection on the significance of delaying previous deals.”
Israel’s military spokesman, Rear Admiral Daniel Hagari, said the four men had died together in the southern Gaza city of Khan Younis when Israel was operating there.
He said: “We are checking all of the options. There are a lot of questions.”
Hamas claimed in May that Mr Popplewell died after being wounded in an Israeli airstrike, but did not offer any evidence to support the claim.
Hamas took some 250 hostages back to Gaza after their attack on Israel on 7 October, during which the group also killed around 1,200 people.
More than 100 hostages were released during a ceasefire in November in exchange for Palestinians imprisoned by Israel.
Of the roughly 130 remaining in Gaza, about 85 are believed to still be alive.
The Israeli offensive in Gaza has killed more than 36,000 Palestinians, according to the health ministry in Hamas-run Gaza, and has resulted in a widespread humanitarian crisis in the territory.