DALLAS — Inextricably linked to the death of John F. Kennedy, surgeon Robert McClelland dutifully preserved the blood-soaked white dress shirt he wore the day he tried to save the president’s life in 1963.

For the rest of his life, the retired professor emeritus of the University of Texas Southwestern’s medical school also clung staunchly to a contentious opinion forged firsthand: that one of the shots that had struck Kennedy had come from the front, which would require the existence of a second gunman.

Robert Nelson McClelland, the lone dissenting voice among the operating-room doctors who tried to save the president at Parkland Memorial Hospital, died Tuesday of renal failure. He was 89.

A skilled surgeon whose true passion was teaching, he’s among the luminaries whose images grace Parkland’s walls today. In a note to campus colleagues, Dr. William Turner of the campus’s department of surgery, called McClelland “the titan among those giants,” saying the institution had “lost one of its heroes.”

An insatiably curious reader who doted on his seven grandchildren, McClelland was a driving force in surgical education at UT Southwestern for decades and oversaw the launch of its liver surgery program.

He was modest and unassuming despite his accomplishments and role in history. But he also had an irreverent side, allowing his grandkids as young children to watch the cheeky television show “South Park” with him, to the occasional dismay of their parents.

“I would get angry,” said daughter Alison McClelland of Dallas. “His defense was that it was philosophical.”

Robert McClelland was born Nov. 20, 1929, in Gilmer, the same East Texas town that spawned musicians Don Henley and Johnny Mathis. His intellect and curiosity were evident early, his passion for discovery stoked by a chemistry set he got at age 11.

He graduated in 1947 as valedictorian of Gilmer High and, as the grandson of a physician, was further inspired to pursue medicine through the mentorship of two local physicians.

After studying at the University of Texas in Austin, he earned his doctorate at the school’s medical branch in Galveston in 1954. He spent two years in Germany as a general medical officer for the U.S. Air Force, then returned to Texas to begin residency at what is now UT Southwestern.

It was there that he would meet Connie Logan, a head nurse at Parkland whom he’d noticed several times at church and finally got the nerve to ask out. They married in May 1958 and settled in Highland Park, where they raised three children.

He completed his residency in 1962 and joined the faculty at UT Southwestern and Parkland, where the following year, that momentous November day became forever tied to his life story.

He was 34 then, screening a film on hernia repair for hospital interns and residents, when a colleague burst in and asked him to help operate on the president of the United States.

As Kennedy lay wounded on the operating table in Trauma Room One, McClelland assisted as surgeons Malcolm Perry and Charles Baxter performed a tracheotomy in an attempt to save the president. For 10 minutes, he stood above Kennedy’s head and stared at “that terrible hole,” as he put it, tackling his duty as instinctively as a fireman slides down a pole.

But from his vantage point, one shot seemed to have come from the front — which would mean Lee Harvey Oswald, whom McClelland would be called to operate on just two days later, wasn’t the only gunman.

“The shot that killed (Kennedy) probably was from the back, but I have to honestly say what I think,” McClelland told The News.

The other four attending physicians would eventually pen a joint article in The Journal of the American Medical Association concluding there were two shots, from the back and above. The journal’s editor noted McClelland’s differing opinion, emphasizing, however, that he wasn’t an “expert in forensic pathology and ballistic wounds.”

McClelland never wavered, and a scene from Oliver Stone’s “JFK” depicts him offering his dissenting opinion in court, which McClelland said never actually happened. However, he did once act as a juror in a 2013 mock trial giving Oswald his chance in the courtroom. (The trial ended in a hung jury, with the vote 9-3 in favor of a guilty verdict.)

McClelland would go on to spend his entire career at UT Southwestern, where generations of students and residents knew him as “Dr. Mac” and called him for years afterward seeking advice about difficult cases.

In 1974, he launched the medical journal Selected Readings in General Surgery after requests from former residents for copies of papers discussed in a journal club he’d started. The club eventually became a Saturday morning event, led by McClelland, for the school’s surgery department, with the compilations earning national and worldwide subscribers as they covered the entire field of general surgery.

A prodigious reader, he consumed history books and subscribed to dozens of medical journals.

“He was a very sharp man,” said Scot Sandlin, who with others occasionally met McClelland in his later years for breakfast gatherings at the Flying Fish at Preston Center. “A very factual kind of guy.”

McClelland’s grandson, William Yoste of Oxford, Miss., with whom he would go to movies and enjoy Goff’s Hamburgers, recalled the tales “Pop” would tell him as a child before he went to sleep.

“Instead of reading me bedtime stories about the rabbit and the hare, he would tell me about growing up in Gilmer, or coming to Dallas before it was anything,” Yoste said. “Everything he said to anybody just left you wanting more, hoping that when one story ended another would begin.”

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McClelland adored his hundreds of books more than any other material thing.

“When we moved him, his only requirement was that he had to have a place with bookcases in every room,” said daughter Alison, whose memories of her father as a child were of him behind a pile of journals on his huge office desk, blaring classical music while flanked by his Siamese cat, Bandit.

“We needed to have custom bookcases built. He would give anybody the shirt off his back, but he would never loan out his books.”

Until last weekend, McClelland had remained engaged, reading constantly and asking a million questions about what his family members were up to. Then things took a sudden turn.

By Tuesday afternoon a hospital bed had been wheeled in, around which the family gathered, playing Mozart and screening “South Park” on the TV in tribute. McClelland died peacefully that evening.

In addition to daughter Alison and grandson William, McClelland is survived by his wife, Connie, of Dallas; son Chris McClelland and daughter Julie Barrett of New York City; six grandchildren; and a great-granddaughter.