The Archdiocese of Philadelphia has launched an investigation into allegations that a former student at St. Charles Borromeo Seminary sexually harassed a freshman at the Wynnewood school during the 2010-11 academic year, according to a letter sent Tuesday to priests, deacons and others associated with the seminary.

The letter, signed by Auxiliary Bishop Timothy Senior, stated that the alleged violations of the seminary's sexual harassment policy have been turned over to the archdiocesan director of investigations.

The probe is the result of a series of complaints that "surfaced on social media last week," according to the letter.

On Aug. 9, former St. Charles student John Monaco, 25, of Boston, described his experiences of sexual harassment at the seminary in posts published on churchmilitant.com and on his own blog at medium.com.

The essays recounted sexual harassment Monaco said he endured as a student at St. Charles beginning in the fall of 2010, and also outlined "abuse and misconduct" he later witnessed at St. John's Seminary in Brighton, Mass. Monaco enrolled in St. John's in 2014 after a year at St. Charles and earning a bachelor's degree at a Connecticut college. He identified the seminaries in the two posts after initially writing about the schools without naming them in an essay posted Aug. 3 on One Peter 5, a Catholic website.

Now a graduate student in Boston, Monaco said that as a 17-year-old freshman at St. Charles, he was subjected to sexually inappropriate advances by a fellow student who visited his dorm room. Several months later, he said, he was groped at an off-campus party hosted by a then-seminarian who also gave Monaco a drink that he suspects was spiked because he soon began to feel disoriented and fell asleep.  He also saw two seminarians fondling each other at the party, Monaco said.

When he told his formation director about the experience, Monaco said he was told that he should be more understanding of his fellow seminarians. The formation director then prayed over him.

In a statement late Thursday afternoon, archdiocesan spokesman Ken Gavin said that the seminary only "recently became aware of allegations of sexual harassment by one seminarian of another that is purported to have occurred during the 2010-2011 academic year … In keeping with the long-term policy of the seminary and the Archdiocese of Philadelphia, this allegation was turned over the Archdiocesan Office of Investigations for appropriate handling in light of policy and applicable law. As it is an active investigation, we are not able to comment upon it further."

Monaco said he felt compelled to come forward after reading about Cardinal Theodore E. McCarrick, former archbishop of Washington, who was forced to resign last month from the College of Cardinals following reports that he had sexually abused minors and adult seminarians over the course of decades.

"It was painful to go back and reexperience the memories, but I am glad that I came forward …. A seminary should never be a place where a man does not feel that he can be protected and grow in holiness," Monaco said from Boston, where he is studying for a master's degree at the Boston College School of Theology and Ministry.

At St. John's, Monaco said, he witnessed excessive drinking by students and faculty, and seminarians "cuddling" in the "downstairs" common room. He heard about "sexting" by a student who was seeking "hookups," and about priests who would get drunk and invite a special "clique" of seminarians to their rooms for private parties.

He was so troubled by his experiences at both schools, he said, that he sought counseling.

Cardinal Sean O'Malley, archbishop of Boston, announced an investigation into the allegations at St. John's in a statement released Aug. 10.  Another former St. John's student also has come forward with complaints of inappropriate behavior. The seminary's rector has been asked to go on an immediate sabbatical during the investigation, O'Malley's statement said.

The allegations come as the Catholic Church in Pennsylvania is reeling from the release of a grand jury report that outlines child sex abuse involving more than 1,000 victims and hundreds of priests in the state over decades. The report includes witness testimony and complaints against priests in the Dioceses of Pittsburgh, Harrisburg, Allentown, Scranton, Erie, and Greensburg.

>>READ MORE: Pa. Catholic Church sex abuse report names hundreds of priests, accuses leaders of cover-up: 'They hid it all.'

The Philadelphia Archdiocese and the Altoona-Johnstown Diocese were not included because they had earlier been the subject of grand juries that examined sex-abuse claims against clergy.

St. Charles expects more than 170 seminarians to enter with the start of this school year.  About 50 of them are new students, the letter said. The archdiocese distributed the letter to remind priests and deacons about the policies regarding "sexual violence, harassment and stalking," as officials prepare to welcome the incoming classes. The regulations will be reviewed by seminarians and each will be required to sign a form acknowledging that he has been informed of the policy.

All allegations are to be reported to the Seminary Department of Safety and Security, which will then turn them over to the archdiocesan director of investigations. Allegations against clergy are reviewed by the Archdiocesan Professional Responsibilities Review Board. Any alleged criminal conduct is reported to law enforcement before an archdiocesan investigation proceeds, according to the letter, which was first posted by Catholics4Change, a group that advocates for church accountability.

Monaco recalled his time at St. Charles as "toxic" and said he has been contacted by former students who agree with his depiction of seminary culture. He described it as a cloistered, solitary experience that felt like prison at times. He said he no longer wants to be a priest, but remains a devoted Catholic.

"There was no real interaction with parishes, the average Catholic person, or other Catholic universities, or other Catholics our age. It was like we were in our own little island in the middle of Wynnewood," said Monaco, who is studying to teach theology.  "That's not what you want for your future priests."