The line below is taken from an article published in The New York Times.
In 2012, Fran Lebowitz, the humorist and noted nemesis of Michael Bloomberg, who was then New York City’s mayor, sneered that the billionaire businessman and philanthropist could not stand the thought of someone having a bigger job than his.
I can't understand weather the phrase
who was then New York City’s mayor refers to Fran Lebowitz or Michael Bloomberg. Please help me figure this out.