Different drama, same fate: how Billy's death in The Halcyon echoes the plot of Downton Abbey

But that doesn't mean we were ready for what was coming.

We started getting nervous for Billy (Ewan Mitchell) in episode six when he stepped up his wooing of hotel maid Kate Laughlin (Lauren Coe), who fits neatly into the shoes/apron of Downton kitchen maid Daisy.

Except, unlike Sophie McShera's Daisy, Kate seems to have genuinely fallen for her war hero suitor. Apparently, the secret is an orange.

Yes, a rare citrus fruit is all it takes for Billy to get a kiss – presumably his first, judging by the way he says "bloody 'ell" and tugs at his collar as he struggles to process what just happened. But with a scarcity of exotic fruits in England in 1940 ("not even Feldman can get oranges!"), it's admittedly quite a romantic gesture.

Instead of gobbling the gift down like any other vitamin-C deficient wartime Londoner, Kate instructs Billy to meet her the next morning before her shift so they can romantically share her orange.

Unfortunately, that means both of them have to survive another night of the Blitz, so Billy heads off to man the anti-aircraft guns.

Let's recap: earnest soldier arranges a date for the next day with the woman he loves, and then goes out to heroically fight the enemy... you can guess what comes next.

Kate's waiting at the entrance with her precious orange for her lover who will never come home, his mum Peggy is sobbing-screaming to herself, and a bloody dead body is being covered up with a sheet.

William Mason and Billy Taylor may be separated in time, but their storylines are almost a mirror image. Neither was meant to go to war, but both did – driven by a sense that it was their duty, and an adventure.

Downton's William was the only surviving child of Mr Mason. He wanted to sign up but was initially excluded from the war when the Dowager Countess invented a horrible skin condition for him. Despite her efforts, William went off to fight, returned injured, and soon died (at least he got to marry his sweetheart Daisy, even though she wasn't in love with him).

The Halcyon's Billy also had an opt out, even though he didn't like it. Peggy and hotel manager Mr Garland tried to save him from the dangers of front-line conflict by keeping him close to home ("we look after our own" – how Dowager-esque), but did not expect London itself to become so treacherous.

There is something slightly derivative about the whole storyline, admittedly. But even having guessed what was coming, it was impossible not to be moved by Peggy's pain and Kate's horror and the human cost of the war, which we have seen gradually build up over the course of the series.

More than that, it's a tale that rings true. Just as in the First World War, millions of young men in the prime of their lives were sent off to die, so it was in the second worldwide conflict of the 20th century.

History is unoriginal and repeats itself – and so do historical dramas.

The Halcyon continues at 9pm on Mondays on ITV