When Chris Mancinelli walked into his father’s home for the first time after the 79-year-old man died last summer, he stopped to look at family photos displayed on the refrigerator door. Near a crayon drawing spelling out “grandpa” in rainbow colors were photos of his father’s three granddaughters at a swimming pool.

But one image jumped out: a photo of Alexa Bliss, a professional wrestling personality.

Mr. Mancinelli’s father, Alfred, was completely smitten with the star — or at least with the con artist impersonating her. He was convinced he was in a romantic relationship with Ms. Bliss, leading him to give up about $1 million in retirement savings (and his granddaughter’s college fund) to the impostor and a varied cast of online fraudsters he interacted with over several years.

When Mr. Mancinelli tried to intervene, moving his father’s last $100,000 to a safe account, Alfred sued him — his loyalty was to “Lexi.”

“There was nothing we could do to convince him,” said Mr. Mancinelli, 47, a chemical engineer in Collegeville, Pa. An elder care specialist deemed Alfred “really sharp,” he said, but lacking purpose.

Mr. Mancinelli and others who have tried to awaken their loved ones from this trance often feel powerless, even after they’ve done everything to shatter the fiction and protect their assets. They say it’s as if their parent had been brainwashed into a cult.