LANSING, Mich. — The author of a book on Catholic teaching regarding homosexuality and chastity is accused of forming a sexual relationship with a minor about 15 years ago.

Daniel Mattson is the author of the 2017 book Why I Don’t Call Myself Gay: How I Reclaimed My Sexual Reality and Found Peace. He is a frequent speaker on the Church’s teachings on homosexuality. He is closely associated with the apostolate to same-sex attracted individuals and their families, Courage International, and appeared in the 2014 documentary Desire of the Everlasting Hills.

On Monday, a man alleged on Twitter that he and Mattson began in the early 2000s an online relationship that eventually included sexual interaction via webcam and phone. No physical contact is alleged to have taken place.

The man said Mattson provided him with prepaid telephone callings in order to keep the phone sex a secret from his parents. The two spoke almost daily for three or four years, the man alleged.

He said that the relationship began when he was 13 and Mattson was around 30.

“He knew I was only 13,” the man tweeted Jan. 28.

Eventually, the man alleged, the relationship came to an end. He said Mattson had a relationship with a woman, and the two stopped talking.

“Dan now tweets about homosexuality being a sin. He seems kind and only wants ‘children of God’ to be treated with dignity/respect. But he still believes my relationship with my husband is a sin,” the man tweeted. “He needs to understand that he has a responsibility. He's hurting young kids [sic] lives.”

Mattson did not respond to a request for comment.

Mattson’s book recounts his own experience with homosexual attraction. He has said that he had his first homosexual experience at age 32, and that eventually, after dating a woman because of his desire for family life, he converted to Catholicism and embraced the Church’s teachings on homosexuality, committing to live chastely.

It is not yet clear whether Mattson will face charges in connection to the man’s allegation.

Father Philip Bochanski, the executive director of Courage, said he was “devastated” to learn of the allegation against Mattson.

“The same afternoon that I learned of this very disturbing situation, I immediately reported the information I had to the Safe Environment Coordinator of the Diocese of Bridgeport [the Connecticut city where the Courage Office is located] and to the Child Protective Services office of the State of Michigan [where Dan resides], as I am required to do by civil law and diocesan policy,” he said in a Jan. 30 statement.

Mattson has never been an employee of Courage International, but has shared his story at conferences organized by Courage, and in Desire of the Everlasting Hills, which Courage International produced, Father Bochanski said.

He noted that the alleged misconduct occurred “more than 14 years ago, years before [Mattson’s] involvement with the Courage apostolate,” and said that neither he nor his predecessor, Father Paul Check, had previously received sexual allegations against Mattson.

“Mattson will not be invited to speak or write, or to take any leadership positions, on behalf of Courage International for the foreseeable future,” Father Bochanski said. “I will reserve further comment on this matter until the civil authorities have made a final determination in the case.”

“I know how painful this news will be to many people, particularly those who are survivors of abuse in their own lives or in the life of a loved one,” Father Bochanski said. “I am praying earnestly for a just resolution to this matter, and particularly for the needs of the man who has brought this situation to light. I urge anyone who is aware of an incident of sexual misconduct or any kind of abuse involving a child, youth or other vulnerable person, to contact civil authorities immediately.”