Athletic Bilbao prevailed in their Europa League quarter-final tie against Rangers tonight.
This would be enough to please Celtic fans, as is the nature of the intense Glasgow rivalry.
An extra smile will be put on their face when they spot that some Athletic Club fans donned Celtic colours in the stands at the San Mames for the game this evening.
Photos show a Scotland flag, as well as Irish tri-colours on display.
And in amongst all of the red and white sea, green and white hoops could be spotted.
A Celtic kit from circa 2007, with a Carling sponsor on the front of it, could be seen in the stand behind the goal where Nico Williams scored the winner.
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It comes after Athletic Bilbao fans who visited Glasgow for last week's first leg at Ibrox, were seen at Celtic Park during the 5-1 win over Kilmarnock at the weekend.
It follows just two days after Celtic colours could be seen among the visiting PSG fans at Villa Park for their Champions League tie.
