History is full of episodes that make us wonder: what would've happened if things went slightly differently?

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The story of a Spanish spy and his wife ahead of World War Two D-Day operations, just unveiled by secret files released from the National Archives, is one of those big "What ifs...".

Self-made double agent Juan Pujol, codenamed Agent Garbo, was instrumental in feeding misinformation to the Germans about the timing and location of the D-Day landings.

While working for the British MI5, Pujol persuaded his German spymasters that he ran a network of agents in Britain and that the June 6, 1944, landings would take place at Pas de Calais, not Normandy.

But a row with his wife Araceli Gonzalez de Pujol almost changed the course of history. From the documents it emerges that Gonzalez was a badass woman in a world dominated by alpha men spies.

In the early days, it was Gonzalez who helped convince Garbo's German spymasters that he was spying in England - while the two were actually living in Portugal. And it was Gonzalez who established links with the American secret services after unimpressed British embassy officials turned down Garbo's offer of his services.

The couple eventually moved to England and were placed along with their infant son in an MI5 safe house in Harrow, north-west London, to protect Garbo's identity. That's when the trouble started.

Allied landing operations in Normandy, 1944.Credit: ASSOCIATED PRESS

From the beginning, the woman, who, like her husband didn't speak English, was left alone, homesick.

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Unable to make friends in the Spanish community in London -- MI5 feared they'd be influenced by pro-German Spanish agents -- Gonzalez complained about the English weather.

She also hated wartime British food, complaining there was "too much macaroni, too many potatoes, not enough fish." Garbo's bilingual case handler, Tomás Harris, reported that "she grumbled that she had not a single friend here, that her husband would not let her mix with Spanish women in London, nor correspond with her Spanish friends in Spain."

The tipping point was when Gonzalez was denied her desire to go back to Spain and see her mother.

"She has for many months begged me to make arrangements for her to return to her home town, even for a week," Harris reported.

"As her state worsened, she became more desperate and … threatened she would leave her husband. As this did not produce the desired effect, she threatened to take action which would spoil the work and leave her free to return.”

After screaming to Harris that she didn't want to live five minutes longer with her husband, Gonzalez threatened: "Even if they kill me I am going to the Spanish embassy."

At that point, Agent Garbo decided to take action and concocted a false story about being arrested and imprisoned in a detention camp as a consequence of her outburst.

Tricked into believing the ploy, Gonzalez was even taken to visit him, blindfolded, in detention. After the meeting, she signed a statement saying she'd stop asking for permission to return to Spain.

"She returned home very chastened to await husband's arrival," Harris reported.

And so the D-Day landings in Normandy went on, contributing to the Allied forces' victory in Europe.

The recently revealed documents show the sacrifices individuals made -- while Gonzalez was crucial to her husband's success, she paid a huge cost for his work, the National Archives points out.