A Du Pont family heir who pleaded guilty nearly six years ago to raping his 3-year-old daughter was never put behind bars because a Delaware judge ruled he “would not fare well” in prison, court records show.

Robert H. Richards IV — scion of the family who built the chemical empire and kin to the co-founders of a prestigious law firm, Richards Layton & Finger — was given eight years probation and was ordered to seek treatment after being convicted of fourth-degree rape in 2008, the records show.

Officials managed to keep the case away from the public spotlight until this month — when his ex-wife, Tracy Richards, filed a lawsuit seeking compensatory and punitive damages for abusing their daughter and son, the News Journal reported.

Richards, 47 — whose great-grandfather is du Pont family patriarch Irenee du Pont — has never been criminally charged for crimes against his son.

The recently filed litigation claims that the father — who lives in a $1.8 million mansion near Winterthur Museum — raped his daughter, now 11, several times beginning in 2005, according to the newspaper.

Two years later, when the girl was 5 years old, she told her grandmother, Donna Burg, that she was being sexually abused by Richards, court documents show.

The little girl said her father told her it was “our little secret,” but said she didn’t want the man touching her anymore, according to the court docs.

Tracy Richards, after Burg told her of the sickening abuse, confronted her then-husband and had him arrested for raping the child.

Richards used “his family’s wealth and position in the community” to hire an expensive defense team and denied the charges, according to the lawsuit obtained by the News Journal.

But after failing a polygraph test, he admitted to abusing the little girl. Richards allegedly told investigators “he was ill and that he needed medical treatment,” the lawsuit said.

Richards pleaded guilty in 2008 to fourth-degree rape — a deal that helped him dodge any jail time.

Superior Judge Jan Jurden sentenced Richards to eight years in prison, but suspended the time for probation that requires monthly visits with a case officer.

“Defendant will not fare well in Level 5 setting,” Jurden wrote in her sentencing order. In Delaware’s correctional system, Level 5 is prison.

Brendan J. O’Neill, a Delaware public defender, told the Detroit Free Press that the ruling may prompt the public to be skeptical of “how a person with great wealth may be treated by the system.”

But he defended the judge’s decision, saying sometimes people need help more than they deserve to be punished.

“It’s an extremely rare circumstance that prison serves the inmate well,” he told the paper. “Prison is to punish, to segregate the offender from society, and the notion that prison serves people well hasn’t proven to be true in most circumstances.”

But now Richard’s ex-wife is seeking justice by suing him for assault, negligence and negligent infliction of emotional distress on his two children, the News Journal reported.

The lawsuit claims that while taking another lie detector test in 2010, Richards allegedly told the examiner he began to sexually abuse his son in 2005 — when the boy was 19 months old.

The father allegedly confessed that he “was very concerned something happened with his son, but that he has repressed the memories,” according to the lawsuit.

Saying the abuse was “similar to what happened with his daughter,” Richards allegedly “promised that whatever I did to my son, I will never do it again,” the lawsuit said.

An attorney for the convicted pedophile’s ex-wife said the lawsuit is the first step in seeking justice.

“This self-confessed, admitted rapist and child abuser didn’t go to jail and, in fact, he stays in luxury where he’s always been,” said the lawyer, Thomas C. Crumplar.