It seems that Bono made a surprise appearance Tuesday night in Germany, singing with his longtime friend Herbert Gronemeyer at the Metropolis Hall in Potsdam. We got an email this morning from @U2 reader Jules K., pointing us to a couple tweets and Facebook posts about it. And now our friends at U2tour.de are also reporting it.
From all accounts, Bono and Gronemeyer sang his song, "Mensch," the same song they performed together in 2007 at an anti-poverty concert in Rostock, Germany. This tweet mentions Bono's performance last night, but includes a photo of Bono and Gronemeyer from 2007. Another tweet includes a photo from last night's appearance.
The performance was apparently recorded for Gronemeyer's upcoming English-language album, I Walk, which is due for release in October. According to U2tour.de, Gronemeyer will do another concert in London on October 28th, and Bono may make another appearance with him.
UPDATE: U2tour.de has updated its news to include that Bono and Gronemeyer also sang "Stuck In A Moment You Can't Get Out Of" together.