The 49-track demo collection was smuggled out of wherever [studio/publishers/management delete where applicable] in early 2007 and five tracks - "In My Arms", "Fall for You", "Stars", "Lose Control" and "Sensitized" - appeared online over the week leading up to Kylie's birthday at the end of May. In response, Parlophone went after some fans who had been known to have distributed some Fever and Body Language demos in the preceding years and threatened them with legal action, rather than just running with it and harnessing the positivity from the material. I don't think "In My Arms" was ever confirmed to be the lead, but it was likely in the running, as was "The One".
The rest of the X demos dripped out in batches every few years, some in 2010, then a few more in 2014 (exact same day Kylie's Reddit was, and I actually asked her how she felt about leaks, and she replied), and then the whole lot finally surfaced in mid-Janaury 2017.