Alcoyano come from a small town near Valencia, and they have not played in the top league in Spain since 1951. Normally their home ground of the El Collao stadium holds less than 5,000 fans, but, sadly for them, none were present to watch their famous victory in person.
Current health regulations in Spain mean all matches have to be played behind closed doors.
Amazingly, it was the fifth time that Real, who have won the cup 19 times in their history, have been knocked-out of the competition by a third division team.
And the defeat heaps more pressure on Zinedine Zidane, with fans and commentators causing him to be sacked.
They lost at home to Athletic Bilbao in the Spanish Super Cup, and, although they are second in the league to neighbours Atltico, they trail them by four points. To make matter worse, Atltico have two games in hand.
Real did not even have the excuse of fielding a weakened team. Although he did not even start all his stars, the starting XI was still full of internationals. And he had the luxury of being able to throw on the likes of Eden Hazard, Karim Benzema, and Toni Kroos in extra time as his side went in search of the winner.
Real had even taken the lead before half-time through defender Eder Milit0, but, ten minutes from the end of normal time Jose Sorribes popped-up with the equaliser, forcing extra time to be played.
When Alcoyano were reduced to ten men following the dismissal of . Ramon Lopez for a foul on was sent off for a foul on the Brazilian Casemiro, it looked like their brave effort might be in vain.
However, then, with penalties just five minutes away, Juanan escaped his marker at the near post and flicked home the winner.