Parton called in, while Mayer sang Cohen's favorite Diana Ross song in celebration of the Watch What Happens Live host's 50th birthday. Mayer, one of Cohen's closest friends, was also the surprise guest-host for Cohen's tribute. ALSO: Cohen and Mayer revealed they recently smoked pot with George R.R. Martin.
TOPICS: Watch What Happens Live with Andy Cohen, Bravo, Andy Cohen, Dolly Parton, George R.R. Martin, John Mayer, Late Night