The twin’s bodies were only formally identified five days ago thanks to the help of forensic archaeologists.
Gavin Heller told the BBC: "They just found remnants of Liel... initially they didn't have enough pieces to make a formal identification. They identified her literally by sieving the remnants. This will unfortunately live with me for the rest of my life."
Heller’s family is being supported by family liaison officers attached to the Metropolitan Police Counter Terrorism Command.
In a statement issued through the force, Heller said: "I am utterly devastated by the news of my children's deaths in Israel; it has broken me.
"Yannai and Liel had their entire lives ahead of them, but they were cruelly and brutally murdered on that fateful October 7. My life will never be the same.
"There are no words that can ever or will ever explain this pain and brutality. The unfathomable, unimaginable, unspeakable has happened to my gorgeous children, and the world has turned against humanity."
The immediate family of the twins and aunt, Ila (Illios) Hetzroni, during their funeral and farewell-ceremony at Kibbutz Revivim
Recalling the moment that the twins were finally identified, Heller told the BBC: “I was literally inconsolable with grief, not finding her body and at least having something to bury.
“It's something that is such a shock that people can do this to other human beings just because they were Jewish.
"There was no other reason why these Hamas terrorists came in the kibbutz other than to kill, murder, maim Jewish children, babies, parents and old people all because they lived in the Jewish homeland."
Heller said Liel was "a bundle of energy, an extrovert” who loved to perform. He said she was “like a princess and liked to be the centre of attention."
Meanwhile, the father described Yannai as a "very sporty child who loved tennis, football and basketball."
Heller added: “He had a shyness about him that I think everyone respected... he was a lovely boy who was really coming into his own in terms of his character and personality. He mourns the life the twins will not now have.
"They really loved each other and unfortunately they will never be able to live their life to do what they wanted to do in the future and that really is a crying shame, an absolute tragedy... I won't watch them grow up, I will never see them get married, I will never see them flourish as normal teenagers would."
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