"The Celebrity Apprentice" alums have taken to Twitter and Instagram to pay tribute to "The Celebrity Apprentice 2" winner Joan Rivers, who passed away at Mount Sinai Hospital in the afternoon of Sept. 4, Thursday.

The Trump Organization president Donald Trump himself took to Twitter to pay tribute to the 81-year-old veteran comedian and "Fashion Police" host.

"Joan Rivers @Joan_Rivers was an amazing woman and a great friend. Her energy and talent were boundless. She will be greatly missed," Trump tweeted.