Before he died, William F. Buckley Jr. put his young grandson on the firing line.

The intellectual conservative icon – renowned for his erudition and use of uncommon words – excluded his son’s illegitimate child from his massive estate, insisting the kid was dead in his eyes.

“I intentionally make no provision herein for said Jonathan, who for all purposes . . . shall be deemed to have predeceased me,” Buckley’s will says, according to the Hartford Courant.

The National Review founder and notable New Yorker instead left his entire estate – estimated to be worth tens of millions of dollars – to his only child, Christopher Buckley, and Christopher’s two older kids, Caitlin and William.

Jonathan, now 8, is the product of an Christopher’s affair with book publicist Irina Woelfle.

Caitlin, 20, and William, 17, are the author and former presidential speechwriter’s children with his now-estranged wife, Lucy.

Woelfle currently works as a publicist in Florida, where she filed suit against Christopher, seeking more child-support money.

Christopher, 56, author of the satiric novel “Thank You for Smoking,” pays $3,000 a month. But Woelfle’s petition says their son has special needs, and she’s looking to put him into a private school near her Coral Gables home.

The suit, which was obtained by the Courant, pins the blame for some of the boy’s behavioral problems on Christopher’s complete lack of involvement.

“The father is notably absent from the minor child’s life,” despite the mom’s efforts to try to get him involved, the suit says.

“As Jonathan gets older, he requires love, attention and a notable involvement in his life from his father,” the suit says.

“It is in Jonathan’s best interest and welfare for this court to impose a contact and access schedule on the father, so that Jonathan can establish a relationship with his father and extended paternal family.”

The filing says the boy has been diagnosed with attention deficit hyperactivity disorder, and needs a school with a “small, nurturing classroom setting.”

The filing says Christopher should pay for the school, and makes note that “there has been a substantial change in the father’s income” since they reached a child-support agreement in 2003.

The Courant estimated the value of William Buckley’s estate at more than $30 million.

Jonathan’s grandfather wasn’t alone in turning his back on the boy, the report says.

In his original settlement agreement with Woelfle, Christopher did not want visitation rights. The deal prohibited Woelfle from contacting Christopher directly about Jonathan, and said all communication should go through their attorneys.

Christopher currently lives in Washington. It is unclear when his father, who died in February at age 82, wrote his will.

Woelfle and Christopher’s lawyer did not return calls.

dareh.gregorian@nypost.com