An ex-Marine who took his semper fi spirit to Syria to fight alongside a US-backed Kurdish militia group in the battle against ISIS has been killed.

David Taylor, a 25-year-old Floridian, had kept mum about his plans to join the People’s Protection Units, or YPG, after he was discharged in 2016 — telling only one pal, whom he swore to secrecy.

His own father only found out when his son arrived in Syria last spring and began training.

“I got an email and he said, ‘Pops, don’t worry. I’m with the YPG,'” David Taylor Sr. told the Associated Press from his West Virginia home. “He said, ‘I’m doing the right thing. It’s for their freedom.'”

Taylor Sr. said his son never wavered in his goals.

“There was no middle ground. He wasn’t wishy-washy,” said the dad, adding that a UN consular official told the family of Taylor’s death last weekend.

Taylor’s high school friend said the leatherneck told him during a visit to St. Petersburg Beach, Fla., last February that he believed that ISIS had to be stopped.

“One night he got drunk and told me of the atrocities he had witnessed in the Middle East during his time in the Marine Corps,” the friend, Alex Cintron, wrote in an email to Taylor’s parents.

“He said to the effect that ‘ISIS was the bane of modern existence and needed to be stopped before they destroy any more lives and priceless works of human achievement,'” Cintron wrote.

He said Taylor was killed by an improvised explosive device.

A Kurdish militia group has released a video saying Taylor was “martyred fighting ISIS’ barbarism” on July 16, but offered no details on how he lost his life.

Taylor, who grew up in Ocala, about 80 miles northwest of Orlando, attended college in Florida and West Virginia before joining the Marines.

He had been deployed to Afghanistan, Japan, South Korea and spent time in Jordan, David Taylor Sr. said.

Last spring, he asked his dad to drive him to the airport because he wanted to visit Ireland, where his family has ancestral ties.

Taylor Sr. received sporadic updates from his son about his travels in Europe until he heard nothing for several weeks. Soon afterward, the elder Taylor received an email from his son, saying he had joined the militia group.

The consular official told Taylor Sr. that the YPG is covering the costs of transporting Taylor’s body back to the US.

“He loved his country. He loved democracy,” the father said. “He had a mission, to go over there and advance democracy and freedom like we have it over here. It came at a horrible price.”

The US State Department said in a statement that it was aware of reports of a US citizen being killed while fighting in Syria but offered no further comment.

Two other Americans were recently killed in Syria during a battle to retake the terror group’s de facto capital of Raqqa.

Robert Grodt, 28, a former Occupy Wall Street activist from New York, was killed July 6.

He had joined the YPG to fight the extremists in Syria, where he had adopted the moniker Demhat Goldman, CBS News reported.

The other American killed was Army veteran Nicholas Warden, 29, who had adopted the Kurdish name Rodî Deysie. He was killed July 5 while fighting around Raqqa, the network reported.

With Post wires