Dave Grohl's bad mood at Wimbledon now makes sense ... the rocker stepped out with his wife, Jordyn Blum, at the tournament weeks before confessing he's fathered a baby outside his marriage.
Check it out ... the Foo Fighters frontman had a blatantly snippy attitude while being interviewed at the London tennis event back in July.
In the footage, a BBC Sport reporter politely asked Grohl for any final predictions for the tournament at the All England Lawn Tennis and Croquet Club .