Next month the UK Competition Commission is to rule on whether Ryanair must divest some or all of its near-30% stake in Aer Lingus, a new twist in a long-running legal battle between the two carriers.
Having already stated in its investigation that Ryanair's holding could "influence the commercial policy and strategy" of the Irish flag carrier, and that a merger could reduce competition on routes between the UK and Ireland, the commission is widely expected to force Ryanair to divest its holding.
So, does this leave Michael O'Leary's dream of taking full control of Aer Lingus in tatters? Not necessarily.
If the commission forces Ryanair to take its holding below 5%, the budget carrier will be prevented from calling extraordinary general meetings and blocking special resolutions at shareholder meetings - but it can still launch takeover bids.
A ruling that Ryanair must sell down its entire stake would leave Aer Lingus relatively safe from such bids. But as a publicly listed company, Aer Lingus could never rule out Ryanair returning as a minority shareholder and the whole process beginning anew.
And O'Leary has no intention of doing anything but fight.
Today, the Ryanair boss launched a virulent attack on the very foundation of the UK Competition Commission's investigation.
"This misguided UKCC inquiry is a political farce which has no case, no evidence and no credibility," he said.
"Having been asked by the OFT [Office of Fair Trading] to check if competition has been lessened, even the UKCC has now been forced to accept that competition between Aer Lingus and Ryanair has intensified."
To prove his point, O'Leary revealed that his airline would be launching five additional frequencies on UK routes from Dublin this winter. Aer Lingus is a rival on all five.
Earlier this week, Ryanair's finance chief Howard Millar told Flightglobal Pro that there would be an appeal if the commission's decision went against the budget carrier, and that the case would "run and run and run".
And it is not just a simple matter of making Ryanair sell its stake in Aer Lingus. The question is: who would buy it?
Ryanair has very publicly announced it would sell its stake in Aer Lingus to any European airline that could secure 50% of shareholder approval. To date, it says, no one has come forward.
This means Ryanair will likely hold on to its stake until forced to give it up in a fire sale by the Competition Commission.
But the UK case is just one part of the legal struggle between the two carriers.
The saga began 2 October 2006 when Aer Lingus shares were first floated on the Irish and London stock exchanges. Within three days, Ryanair had acquired a 19.1% holding, and it immediately declared its intention to launch a public bid for Aer Lingus. It did so that same month.
In 2007, the European Commission blocked the bid on competition grounds. Ryanair launched a further two unsuccessful bids to take full control of Aer Lingus, in 2008 and 2012.
In each case, Ryanair has been forced to wait a set time before being allowed to bid again, but there is nothing preventing it from making more bids.
It is also easier for Ryanair to attack than for Aer Lingus to defend itself. Ryanair says it has spent some €4 million ($5.3 million) in legal fees on its three failed takeover bids, but Aer Lingus has shelled out €40 million to counter them.
A major blow for Aer Lingus came in the Irish courts this month, when it lost an appeal aimed at preventing Ryanair from launching another takeover bid a year after its third bid in August 2012.
The Irish flag carrier argued unsuccessfully that its low-cost rival should have to wait until February 2014 - 12 months after its bid failed - to mount a fresh assault. The upshot is that Ryanair can once again assay a takeover as early as next month.
For O'Leary, there is still everything to play for.