Mel Greig's Celebrity Apprentice co-star shared a tweet calling her a "murderer."

“I’m so astonished and disappointed.”

Mel Greig has voiced her dismay at a cruel tweet that labelled her a “murderer” and was shared by one of her co-stars.

Radio personality Greig, a current The Celebrity Apprentice contestant, was involved in a 2012 on-air prank linked to the suicide of British nurse Jacintha Saldanha.

Yesterday, Greig’s Celebrity Apprentice co-star Richard Reid retweeted a hurful post that apparently referred to that tragic incident.

“Not really happy about a Murderer being on Celebrity Apprentice,so I am out, your fired Mel Greig,” the post read.

On seeing that he had retweeted it, Greig hit back at Reid, questioning his motives.

“Richard I’m so astonished and disappointed that you would retweet this? Murderer?” she wrote on Twitter.

Reids quickly apologised, sending a series of tweets to explain he was simply on a “retweeting roll” at the time.

“I am so so sorry about this Mel – I was on a retweeting roll of both good and bad and thoughtlessly retweeted it,” he explained.

“Mel I was on a retweeting ROLL and didn’t think before I hit the button, I retweet the good AND the bad. It was completely thoughtless,” he continued.

“Lesson learned.”

But Greig has not publicly accepted the apology.

Her last activity on Twitter involved favouriting and retweeting comments saying of Reid: “he is a dick” and “absolutely disgusted”.

Greig has previously spoken of her distress surrounding Saldanha’s death, which followed a hoax call in which Greig and Christian impersonated members of the royal family.

During the prank, the radio DJs called the hospital at which Saldanha worked to gain information about the Duchess of Cambridge’s labor.

The nurse fell for the prank and transferred the call to the nurse in charge of the Duchess.

Saldanha, who had reportedly attempted suicide twice prior to her death, was reported to have left a note partially blaming the radio prank for her suicide.

After Saldanha’s death, Greig appeared on national television to tearfully apologise for the prank alongside her 2Day FM co-host Michael Christian.

Both Greig and Christian ultimately lost their jobs over the tragic incident. In a settlement in 2013, however, Austereo made a public statement that Greig was not responsible for the decision to air the prank call and had suggested it be edited before going to air.

Greig, who in 2014 made a surprise appearance at the inquest into Saldanha’s death, later appeared on Sunrise to say she may never be able to completely forgive herself over the hoax.

“I don’t know how you completely forgive yourself – someone wrote my name in their suicide note,” she said on the breakfast show.

“They thought of me before they took their own life and that will stay with me forever — but I can move forward from that point, I think, because I’ve tried to say sorry.”

Next time, Reid, think before you retweet.