This is the tribute we've all been waiting for... Janet Jackson is rehearsing for a performance honoring her brother for the MTV VMAs.

Janet is expected to open the show on September 13th at Radio City Music Hall. We're sure that it will set the tone for the whole show, which will undoubtedly eulogize Michael Jackson throughout.

Miss Jackson's performance is said to include 20 back-up dancers and sources have told TMZ that some of the rehearsals have lasted 15 hours in a single day!

We were already looking forward to this one (and pulling for the Beasties to win), but now we may have to DVR it to make sure we do not miss the Jackson tribute!