Paul Kelly's Rita Wrote A Letter the latest in a long line of sequel songs

In doing so, Paul Kelly continued the long tradition of sequel songs: a mainstay of pop, rock, hip hop and metal songwriting for decades.

Here are some of the best examples of turning one song into two.

It has already spawned a film and a recurring spot on the Aussie cultural calendar; now Kelly's beloved Christmas single has also yielded a much talked about sequel.

But did you know 'How To Make Gravy' might be something of a sequel itself?

"To Her Door, then 'Love Never Runs on Time', and 'How To Make Gravy' – I've got a feeling it's the same guy," Kelly told Australasian Performing Rights Association's publication APRAp in 2002.

"He keeps coming back … he's a bit of a f**k-up, that guy."

Unfortunately for Joe (or Jack, as he's known in To Her Door), he's no longer around to make the gravy, or any more trouble, having been killed off in 'Rita Wrote A Letter'.

Widely considered the first sequel song of the rock 'n' roll era, 'Peggy Sue Got Married' followed in the footsteps of Buddy Holly's second top five hit in the US.

The original 'Peggy Sue' was written by Holly and his band's drummer, Jerry Allison, about Allison's on-again-off-again girlfriend Peggy Sue Gerron.

Allison and Gerron later married, but Gerron claimed in 2017 in her memoir that Holly was secretly in love with her and had planned to get divorced so they could be together, something vehemently denied by Holly's widow Maria Elena.

The story is made all the more messy by the fact just months before he died, Holly wrote and demoed a song called 'Peggy Sue Got Married', in which he laments that the character from the first song had broken his heart by tying the knot with someone else.

Holly died in a plane crash, aged 22, and the demo for 'Peggy Sue Got Married' was released posthumously with a bunch of overdubs, reaching #13 in the UK and inspiring a 1986 Francis Ford Coppola film of the same name starring Kathleen Turner and Nicolas Cage.

In the early 60s pop music moguls leaned into the notion that if something worked once, it could work again.

When Chubby Checker had a hit with his dance craze cover of 'The Twist', his record label wheeled out a sequel 'Let's Twist Again' exactly 12 months later.

Similarly, after 18-year-old singer Shelley Fabares had a #1 hit in February 1962 with 'Johnny Angel', her label promptly released the sequel 'Johnny Loves Me' just three months later.

So when Lesley Gore's 'It's My Party' hit the Billboard 100 on May 11, 1963, it took just three days for her label to commission and record a sequel, which was released about five weeks later.

Whereas It's My Party details a heartbroken girl in tears after a rival named Judy leaves her party with her lover Johnny, the catchy follow-up 'Judy's Turn To Cry' details the sweet schadenfreude of Johnny ditching Judy and returning to the loving arms of the narrator.

Both songs were top five hits in the US and top 20 in Australia.

Across three epic tracks totalling almost 20 minutes and spanning 17 years, thrash metal icons Metallica explored themes of struggle, sin, redemption, forgiveness, and ultimately self-forgiveness in its Unforgiven trilogy.

The saga starts with 'The Unforgiven' on the self-titled Black Album, a rare song from the "quiet/loud/quiet" 90s that inverts the dynamic by making the verses loud and the choruses quiet.

The track was one of the cornerstones of their mega-selling Black Album (30 million copies, and counting), leading to a sequel titled 'The Unforgiven II' on the sprawling Reload record six years later.

While 'The Unforgiven II' features similar chords and tones, the band tried a different approach for 'The Unforgiven III' on 2008's Death Magnetic, bringing strings, piano, horns and a gothic country guitar lick before the thrash finally kicks in.

In the wake of the break-up of The Beatles, each of the Fab Four worked hard to strike out on their own.

George Harrison did so by digging into Indian music, pushing his songwriting into unexpected directions, and largely ditching Beatles' songs from his setlist, culminating in a 1974 North American tour that was slammed by some elements of the music press, most notably Rolling Stone.

Harrison hit back in 'This Guitar (Can't Keep From Crying)', which even name checks Rolling Stone and hints at his past Beatles hit 'While My Guitar Gently Weeps' in its tone, title and even some of its chord changes.

The songwriter described the sequel song to the BBC in 1975 as The Son Of While My Guitar Gently Weeps, though it strikes a much more pointed yet positive tone than its parent/predecessor.

Harrison did a similar thing again in 1979, by releasing a track called 'Here Comes The Moon', though its similarity to his Beatles cut 'Here Comes The Sun' doesn't extend much further than the shared title.

There are lots of sequels in hip-hop: Part IIs are scattered across albums, and the genre is littered with diss tracks that spawn endless follow-ups.

But this one is different.

Written originally by rapper-producers Angela Hunte and Janet Sewell-Ulepic, 'Empire State Of Mind' is a tribute to the Big Apple, with the 2009 single featuring JAY-Z rolling through New York memories and landmarks as Alicia Keys hits a hook that soars higher than the Chrysler Building.

The sequel is more subtle, stripped-back and intimate, detailing Keys's own perspective of New York, and what it means to her.

Shorn of JAY-Z's braggadocio, it's a fascinating flip on a big hit.

Similarly, the Eminem-Rihanna team-up 'Love The Way You Lie' has a female-focused follow-up '(Love The Way You Lie (Part II)', which amplifies Rihanna's perspective in its exploration of abusive relationships.

David Bowie created many fascinating characters and personas in his career, with arguably the first being the astronaut Major Tom.

The cosmic traveller helped catapult Bowie to stardom in the hit single 'Space Oddity', which merged the era's space-race fascination with psychedelia and endless pop hooks.

But Major Tom's plight was symbolic of Bowie's growing feelings of alienation and isolation.

A little over a decade later, the astronaut returned, this time a strung-out junkie, lost in space, trying to kick his habit, no doubt referencing Bowie's own prior struggles with drugs.

Major Tom also popped up in the Pet Shop Boys' remix of Bowie's 'Hallo Spaceboy' (1996), and appeared in Bowie's farewell film clip 'Blackstar' (2015).

'Mr Brightside' is one of the biggest songs of the 21st century, spending 470 weeks on the British charts, more than 150 weeks in Australia, and selling more than 10 million copies in the US.

So it's probably not surprising Las Vegas rockers The Killers decided to do a follow-up to one of the first songs they ever wrote almost a decade later.

Although the band doesn't seem to have confirmed the song 'Miss Atomic Bomb' is a sequel to Mr Brightside, there are some giveaways.

The signature guitar riff from 'Mr Brightside' appears in 'Miss Atomic Bomb' about three and a half minutes in, and the opening lines of the latter include a reference to the "eager eyes" of Mr Brightside.

But surely the clincher is that the same actors from the 'Mr Brightside' film clip turn up in 'Miss Atomic Bomb', seemingly confirming that it's a continuation of this singalong about lost love and enduring optimism.