The management of Aer Lingus and its minority shareholder Ryanair have never seen eye-to-eye as they have fought to be Ireland’s biggest and best scheduled airline. This relationship took on an interesting twist this week when it emerged that an image of an Aer Lingus aircraft had been used in a graphic to promote Ryanair’s business offering on the budget carrier’s website.

This was quickly picked up by eagle-eyed visitors to the website and soon the news was spreading around social media channels. The Airbus A320, wearing the Irish carrier's retro livery can be seen, although rather blurry, in the background of this screenshot from Ryanair's website.

After discovering the news, Aer Lingus posted the following photo to Twitter of Ryanair’s website, highlighting the image of their aircraft in the background.

The photo was retweeted 677 times, and favourited 571 times with the caption: “Epic #photobomb by EI-DVM on Ryanair’s website! Even they know we’re Best for Business :D” with the image attached and has subsquently led to a lively debate by the two airline's social media teams.

Ryanair hit back by saying Aer Lingus flights are always late:

@Ryanair: “Even @AerLingus is talking about @Ryanair Business Plus. FYI he’s smiling cos he saved a fortune & avoided another late @AerLingus arrival!” the airline tweeted back.

Then, following a Twitter question from @ReallyDes on whether the airlines really do hate each other, Aer Lingus replied that it was just "healthy rivalry”.

Ryanair, Europe’s biggest airline, refused to admit that the two airlines were even equals, claiming that they “stopped being rivals in the 90s.”

@Ryanair: "We stopped being rivals in the 90s. We'd have to treble our fares and lose 81m customers to be your rival #EuropesNo1," the airline tweeted.

Aer Lingus appeared to have given up by this point, tweeting only: “@Ryanair Okay, nevermind. #Peaceout”