VIENNA – R&B stars Mary J. Blige, Akon and Chris Brown and veterans Natalie Cole and Sister Sledge will honor the late Michael Jackson at a concert in Vienna later this month, with more stars due to be announced this week. Thirteen artists so far have been confirmed to perform at the concert, set in front of Vienna’s Schoenbrunn castle on September 26, Michael’s brother Jermaine Jackson and producer Georg Kindel told reporters at a news conference in Vienna. A total of 20 to 25 artists are expected to confirm eventually, they said. More names were to be revealed at separate news conferences in London yesterday and in Berlin today, Kindel said. In front of an expected audience of 65,000 – plus millions on TV screens worldwide – artists will reinterpret Jackson’s greatest hits including Billie Jean, Thriller and Bad.