Real-estate mogul Donald Trump was trolled on Twitter and now wants to sue the prankster whose tweet he retweeted.

What was the tweet?

Phil Bradbury, a comedian, tagged @realDonaldTrump in a post saying that his parents thought Trump was an inspiration, and if he would please retweet in memory of his dead parents, RT.com reported.

The highlight of the prank was an older picture of a couple which was attached to the tweet.

When Donald Trump retweeted to his 2.7 million followers, he was, in fact, sending out a picture of infamous British husband and wife serial killers Fred and Rosemary West.

The Wests tortured, raped and murdered an unknown number of women in the 1970s and 1980s, according to the New Zealand Herald.

They were convicted after being caught in the 1990s for the rape, torture and murder of 10 girls, RT.com reported.

Fred West committed suicide while awaiting trial and his wife is serving a life sentence in the UK.

Earlier this year, the brother of a missing schoolgirl believed to be a victim of Fred West urged Rosemary to reveal what he knows about her disappearance.

The 15-year-old waitress went missing in Gloucester in 1968, the Mirror reported.

Trump's retweet had more than 2,000 retweets before he realized what had happened, RT.com reported.

I thought I was being nice to somebody re[garding] their parents. I guess this teaches you not to be nice or trusting. Sad!" he tweeted. "Some jerk fraudulently tweeted that his parents said I was a big inspiration to them + pls RT-out of kindness I retweeted. Maybe I'll sue."

In response, Bradbury was please with his success in trolling the famous individual.

"Possibly the greatest thing ever to happen to me on Twitter," he wrote.

Soon after, copycats emerged, urging Trump to retweet in memory of their dead relatives. This included characters ranging from serial killer Ted Bundy to Mongolian conqueror Genghis Khan.