In the last days of July 1942, Nazis torched synagogues and seized Jewish businesses in Przemysl, a city in southeastern Poland that had been divided between Nazi and Soviet occupation. As some 22,000 Jews were rounded up for deportation to death camps, 18-year-old Renia Spiegel sat terrified in her hiding place.

“My dear diary, my dear beloved friend!” she wrote in her florid, schoolgirl script in one of the lined notebooks where she recorded her daily thoughts. “We went through such terrible times together and now the most terrible moment is upon us.”

Renia, a Jewish student, had been separated from her parents and younger sister and secreted in an attic on the outskirts of the Jewish ghetto as the Nazis began their death-camp roundups.

“God, protect us all,” wrote Renia. “Into your hands I commit myself. You will help me.”

By the time she wrote those desperate words, Renia’s diary — a journal of school exercise books that she had bound together with thread — was almost 700 pages long. She had started writing it when she was 15 at the end of January 1939, eight months before the German invasion of Poland led to the Second World War.

She kept writing as the chaos unfolded, and days after she recorded her last entry — July 25, 1942 — the diary disappeared.

It reappeared in New York City in the late 1960s but remained unread until just a few years ago. Now, the sheaf of brittle, yellowing pages, covered in fading blue ink has pride of place on the dining-room table of a Manhattan apartment watched over by Renia’s younger sister, a retired New York City schoolteacher who is determined to share Renia’s unique wartime journal with the world.

“I still find it difficult to look at,” Elizabeth Bellak, 87, told The Post. “It’s very painful for me.”

The journal has already been published in Poland, where it has spawned a national poetry competition and drawn comparisons to Anne Frank’s “The Diary of a Young Girl,” although the German-born Frank was only 15 when she died of typhus at the Bergen Belsen death camp. A documentary is in the works about Renia’s life, and the book is currently being translated into English.

Those who have already read the Polish-language journal, in which Renia relates the horrors of wartime pogroms as well as the flowering of her first romance, describe it as an important literary find.

“[It’s] an incredible historical and psychological document, as well as an authentic literary achievement,” Columbia University professor Anna Frajlich-Zajac told The Post. “It’s a great discovery.”

Renia Spiegel was born on June 18, 1924, to Bernard and Rose Spiegel in Uchryńkowce, a village in southeastern Poland. Her father was a landowner and her younger sister, Elizabeth, was known as the Polish Shirley Temple — a precocious star of stage and cinema by the time she was 8.

The Jewish family lived on a large estate near the border with Romania.

“I used to live in a beautiful manor house on the Dniester River,” wrote Renia in her first diary entry on Jan. 31, 1939. “I loved it there. These were so far the happiest days of my life. There were storks on old linden trees, apples shimmered in the orchard and I had cute, even rows in my flower bed.”

But the pastoral idyll came to an end when Rose and Bernard separated. Rose took her daughters to live with their grandparents in nearby Przemysl while she worked in Warsaw promoting Elizabeth’s fledgling acting and singing career.

“Now I live in Przemysl, at my granny’s, but, honestly speaking, I have no home and that is why I sometimes get so sad that I have to cry,” wrote a 15-year-old Renia. “I cry though I don’t miss anything, no dresses, no sweets no strange and precious dreams. I only miss my Mummy and her warm heart.”

Renia is so homesick for her mother that every diary entry ends with her begging her mother, whom she calls Bulus, and God to protect her. “You will help me, Bulus and God.”

Interspersed with her poems, complaints about the mean girls at school, and missing her mother, Renia — a raven-haired teenager with dark eyes and porcelain skin — writes about how a looming war with Germany affects her own life.

“I learn French now and if there is no war, I might go to France,” she wrote on April 2, 1939. “I was supposed to go before, but Hitler took over Austria then Sudentenland, Czechoslovakia . . . and who knows what he will do next. In a way, he affects my life, too.”

Weeks after the Sept. 1, 1939, German invasion of Poland ignited World War II, the Soviet Army invaded the eastern part of the country, and Przemysl became a divided city.

Wartime restrictions prevented Rose from leaving Warsaw, and Bernard, who remained at the family estate, disappeared, likely a victim of marauding Nazis or Soviet troops. Renia and Elizabeth were separated from their mother for two years, stuck at their grandparents’ home in Przemysl.

But by the summer of 1941, as Germany launched its invasion of the Soviet Union, Renia had fallen in love with a student named Zygmunt Schwarzer. Their first kiss took place on June 20, 1941, just as the Germans were preparing to launch that invasion, dubbed Operation Barbarossa.

“We were together, alone, just the two of us,” she wrote in the diary. “The sun had already set, stars began to appear in the sky, the moon came out too and we were sitting next to each other and talking. When we were about to leave, I got all the ways completely mixed up. It was dark and we couldn’t find our way back home. It was such an unexpected and sweet and confounding evening, before Zygo said: ‘Renia, give me a kiss.’ Before I even realized what was going on, he kissed me . . . I felt terribly embarrassed . . . He wanted to kiss me again, but I couldn’t . . . I was all trembling . . . I can’t write anything more now . . . I’ve got to think, think and dream . . .”

By 1942, the relationship between Renia and Zygmunt, who was two years older, seemed to take on a more passionate tone.

“Now I know what the word ecstasy means,” she wrote a few days before her 18th birthday. “I almost understand it. It is indescribable; it is something that is the best, which only two loving creatures can do. And for the first time I felt this longing to become one, to be one body and to feel more.”

But five days after writing about what appears to be the consummation of her relationship with Zygmunt, Renia’s diary is filled with images of chaos and despair.

“Wherever I look there is bloodshed,” she wrote on June 7, 1942. “There is killing, murder. God, for the umpteenth time I humble myself in front of you, help us, save us! God, let us live, I beg you. I want to live! I had so little of life; my life has been so petty, so unimportant, so small. Today I worry about being ugly, tomorrow I might stop thinking forever.”

By June 14, there were more ominous signs: “Panic in the city. We fear a pogrom. We fear deportations.”

A month later, Renia, her grandparents and Elizabeth were rounded up. “Today at 8 o’clock we have been shut away in the ghetto. I live here now; the world is separated from me and I’m separated from the world.”

Zygmunt, who had begun working with the local resistance, managed a few days later to spirit Renia and her sister out of the ghetto in advance of an imminent “aktion,” or liquidation of the Jews, bound for Nazi death camps. At first, they hid in the city’s cemetery. The following day, Zygmunt placed 12-year-old Elizabeth in the care of a Christian family. She was baptized and hidden in a convent before eventually being reunited with her mother in Warsaw. Both of them survived the war.

On July 28, 1942, Renia along with Zygmunt’s parents were hidden in the attic of his uncle’s building at 10 Moniuszki St. Zygmunt’s uncle, Samuel Goliger, was a member of the Judenrat, the Jewish council that the Nazis put in place to administer ghettos throughout the Third Reich. Judenrat members were allowed to live outside the ghetto’s walls.

In her final diary entry, a panic-stricken Renia pleaded with God to protect them.

“Hear O Israel, save us, help us! You have kept me safe from bullets and bombs, from grenades, help me to survive, help us!”

Two days later, on July 30, 1942, Nazis surrounded 10 Moniuszki St., where a frightened Renia and Zygmunt’s parents were hauled outside.

All three were shot dead in front of the building.

A day later, a devastated Zygmunt returned to the house from his own hiding place, and found Renia’s diary. He added his own denouement.

“Three shots! Three lives lost!” he wrote. “It happened last night at 10:30 p.m. Fate has decided to take my dearest ones away from me. My life is done. All I can hear are shots, shots . . . Shots! My dearest Renia, the last chapter of your diary is complete.”

Decades later, no one knows who gave up Renia’s hiding place.

“It’s an enigma,” said Tomasz Magierski, a Manhattan filmmaker who has been researching Renia’s story for the last few years. “We’re not sure if it was the Polish neighbors or members of the Judenrat who gave them up.”

After the war, Elizabeth immigrated to New York City with her mother. Zygmunt did the same — and, years later, found Renia’s family and presented her diary to them.

“My mother was so pleased to have it, but neither of us could read it,” Bellak told The Post as she organized black-and-white photographs of her family on her dining-room table with trembling hands. “I only just started reading it.”

Although Bellak was forced to convert to Catholicism to survive the war — “Religion saved us,” she said — she feels a spiritual bond to her sister reading passages of the diary as Passover approaches this week. “Renia was a very spiritual person,” Bellak said.

It was Elizabeth’s daughter Alexandra, a Manhattan Realtor, who found the diary a few years ago among her mother’s papers and contacted Magierski to help the family research the story.

“We are trying to keep Renia’s legacy alive,” said Alexandra. “Like Anne Frank, she wrote about life during the war but also about mundane things, like being annoyed by her younger sister.”

Magierski said he read the diary in Polish over three days and was so captivated by the writing that he decided to make a documentary film, returning to Poland to piece together the mystery surrounding Renia’s final days.

Now Renia’s family is also cooperating with Zygmunt’s surviving family members to unravel their wartime stories in Poland.

In 1943, a year after Renia’s death, Zygmunt was rounded up and sent to Auschwitz. He survived his internment at the death camp only because its notorious doctor, Josef Mengele, pronounced him fit for slave labor, said Zygmunt’s son Mitchell Schwarzer.

Zygmunt went on to study medicine in Germany after the war and immigrated to New York City in 1949 with his wife, Genia Buchwalter, a Holocaust survivor whom he met while studying medicine at Heidelberg University in 1945. He worked as a pediatrician in Queens until his death in 1992. It’s not clear whether he returned to Poland to retrieve the diary, or whether it was sent to him in America by the Polish Red Cross, Schwarzer said.

“My father was obsessed with the diary,” Schwarzer told The Post. “He spread out photocopies of the pages on his examination table and locked his door and pored over the contents.”

For Magierski, who has traveled back and forth to Poland, promoting the diary over the last three years, the response to Renia’s story been overwhelming.

“This is the best story never told,” he said.