The US software titan had been mocked at previous Apple events as not just an entrenched adversary but as a copycat waiting to duplicate the company's innovations.

Yet Apple chief executive Tim Cook offered the surprise introduction by saying, "Who knows more about productivity than Microsoft?"

Building on the surprise, an Adobe demonstration came in the wake of a presentation by Microsoft executive Kirk Koenigsbauer at the San Francisco event which featured a new iPad Pro and other devices.

"Now Adobe, it's like a parade of conquered rivals paying homage," well-known technology journalist Walt Mossberg of Re/code wrote as he covered the event.

Technology news website Mashable marked the moment with the headline "Hell freezes over: Microsoft makes surprise appearance at Apple event."

The Mashable writer went on to put the Microsoft appearance on par with a Steve Job's nightmare.

Late Apple co-founder Jobs unabashedly fired barbs at Microsoft, which was portrayed as an evil empire overlord while the iconic California was a rebel force.

Microsoft and Apple fans have clashed in San Francisco coffee houses with the kind of intensity though more common for lovers of rival sports teams.

Microsoft's unprecedented appearance on an Apple event stage left those fans to now argue whether it was a sign of Microsoft's defeat in the long-running war or whether Apple needed them as an ally to push iPads deeper into the business world.