The Navy is investigating the death of a SEAL candidate after the 24-year-old sailor died just hours after completing the grueling “Hell Week” test. 

The Navy on Sunday identified Kyle Mullen as the seaman who died at a San Diego area hospital Friday after he and another SEAL trainee reported experiencing symptoms of an unknown illness. 

Mullen joined the military last year. The cause of his death was not known Monday.

The other sailor, whose name has not been released, was hospitalized in stable condition, the San Diego Union-Tribune reported Sunday.

Both men fell ill just hours after they successfully completed the test that ends the first phase of assessment and selection for the elite Basic Underwater Demolition/SEAL (BUD/S) class.

The Navy said neither one had experienced an accident or unusual incident during the 5½-day Hell Week.

Rear Adm. H.W. Howard III, the commander of Naval Special Warfare Command in Coronado, California, offered his sympathies to Mullen’s family in a statement.

“We are extending every form of support we can to the Mullen family and Kyle’s BUD/S classmates," Howard said.

Mullen joined the Navy in March 2021, according to his Navy biography. He reported to SEAL training in Coronado in July, the Union-Tribune said.

Mullen was from Manalapan, New Jersey. He played football at Yale, where he was an All-Ivy League defensive lineman, before transferring to Monmouth University. 

“He will be remembered not just as a excellent player,  but also as an excellent person and a great teammate,” Monmouth coach Kevin Callahan said in a statement. 

Ed Guerreri, Mullen’s coach at Manalapan High School, said, “Everybody loved him.”

“Probably one of the best kids I ever had,” he told USA Today. “Great, great kid on the field but even better off the field.

"Worked hard at everything he did, never gave less than 100%, got along with everybody,” Guerreri added. 

New Jersey Gov. Phil Murphy said during a news briefing Monday that his family knew Mullen “remotely by reputation.”

“He represented the very, very best of our state and our country,” said Murphy, who directed state flags to be flown at half-mast in Mullen’s honor. 

“I never had the honor of meeting him, to the best of my knowledge, but he was a legend, in athletics, in all walks of life,” the governor continued. 

The Hell Week test is part of the BUD/S class, which involves basic underwater demolition, survival and other combat tactics. It comes in the fourth week as SEAL candidates are being assessed and hoping to be selected for training within the Naval Special Warfare Basic Training Command.

The SEAL program tests physical and psychological strength, along with water competency and leadership skills. The program is so grueling that at least 50% to 60% don’t make it through Hell Week, when candidates are pushed to the limit.

The last SEAL candidate to die during the assessment phase was 21-year-old Seaman James Derek Lovelace in 2016. He was struggling to tread water in full gear in a giant pool when his instructor pushed him underwater at least twice. He lost consciousness and died.

His death was initially ruled a homicide by the San Diego County Medical Examiner. A year later, after an investigation, the Navy said it would not pursue criminal charges in Lovelace’s drowning. An autopsy revealed he had an enlarged heart that contributed to his death, and that he also had an abnormal coronary artery, which has been associated with sudden cardiac death, especially in athletes.

It was unclear from the autopsy report how much Lovelace’s heart abnormalities contributed to his death.

The latest death also comes just two months after a Navy SEAL commander died from injuries he suffered during a training accident in Virginia. Cmdr. Brian Bourgeois, 43, fell while fast-roping down from a helicopter, and he died several days later.