"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.

"The Celebrity Apprentice 3" winner Brett Michaels also tweeted, "My deepest condolences to the family of @Joan_Rivers. She was a very funny lady and will be missed. #JoanRivers."

Competing for God's Love We Deliver as her charity, Rivers was 75 when she joined the NBC reality show "The Celebrity Apprentice 2" in 2009 with her daughter Melissa Rivers.

Other celebrity participants were Annie Duke, Jesse James, Brande Roderick, Clint Black, Herschel Walker, Natalie Gulbis, Brian McKnight, Tionne Watkins, Dennis Rodman, Claudia Jordan, Tom Green, Scott Hamilton, Andrew Dice Clay and Khloe Kardashian.

Kardashian, the seventh contestant fired from the competition, took to Instagram to share a photo of her with Rivers with a caption, "Rest in peace Joan!! You will be missed!"

On the other hand, Rivers' rival during the show Duke, who finished second, has yet to comment on her death.

During the final episode of "The Celebrity Apprentice 2" before Rivers was declared the winner over Duke, an angry Duke was recorded saying, "This woman needs to die" referring to Rivers, which was frowned upon by Trump, according to Access Hollywood.

Meanwhile, Melissa Rivers was seen arriving with an entourage at her mother's former house at 5th Avenue two hours after she made a statement confirming her mother's death, Radar Online reported.

Scheduled on Sept. 6, Sunday, the funeral for Rivers will be held at Temple Emanu-El in Manhattan as the temple spokeswoman Elizabeth Fezrine confirmed, but details, including the time and whether or not the public will be allowed to attend, are yet to be confirmed, CNN reported.