The long-discussed dormant fourth button on Hearthstone's main menu screen could soon reveal a new game mode, if a teasing Tweet from Blizzard Entertainment is any indication.

Since the game's post-beta launch in March 2014, Hearthstone's main menu has displayed three buttons representing its major gameplay modes (Ranked Play, Solo Adventures, and The Arena). An allocation for a forth button has always sat beneath this trio, fuelling debate on whether Blizzard was saving the space for a new mode.

On Monday, Blizzard sparked a frenzy of interest from hardcore fans by tweeting a short video clip, which shows the fourth button emerging.

No further details were discussed by Blizzard, meaning that the nature of the new gameplay mode--if it is indeed one--is not clear. In the past, fans of the series have requested many possible features that the popular digital card game could contain.

Hosts on The Legend of the Innkeeper podcast, for example, have suggested the fourth button should be used for an editor, giving players options to build their own games with custom rules and restrictions.

In February, info leaked from a purported Activision source claimed that Team 5 at Blizzard was trialling a new 2vs2 gameplay mode. However, while some details from that story proved to be accurate, some other information had been debunked.

In May, Activision announced that Hearthstone has accumulated some 30 million registered users.