ST. PAUL, Minn. -- Archbishop John Nienstedt, the head of the Archdiocese of St. Paul and Minneapolis, has been accused of inappropriately touching a minor in 2009.

In light of the accusation, the Archbishop will step down from public ministry while the church and St. Paul Police investigate the incident. The accuser alleges Nienstedt touched his buttocks during a "public photo session" following a confirmation ceremony.

"The letter is a real shock," best-selling author John Thavis said.

Thavis lived in Italy and covered the Vatican for 30 years before moving back to St. Paul, where he is writing another book.

"Obviously he is vehemently denying the accusation," the author added.

RELATED:Archbishop denies allegation of inappropriate touching

The archbishop did write a public letter in which he says "this allegation is absolutely false."

The alleged incident was reported to the Archdiocese on Thursday. Nienstedt learned about it Sunday evening and St. Paul Police say they were informed on Monday afternoon.

Nienstedt, also in his letter to the community, wrote "True, I am a sinner, but my sins do not include any kind of abuse of minors. I have met victims and I know the lasting damage such abuse causes."

"I think he realized that the future of his ministry is at stake here, and I think he's really put his reputation, his moral reputation, on the line and he must have confidence that he's going to be cleared," Thavis told KARE 11.

Thavis says it is clear the diocese is taking the matter seriously as it appears to be open and transparent in the process. He also notes that this is a case of a single accuser alleging inappropriate touching, which is far different than some members of the diocese accused of repeated sexual abuse. But Thavis also notes the Vatican is well aware of the accusation and the church will conduct its own investigation while Nienstedt waits for a resolution.

"Sometimes these allegations can be wrapped up rather quickly, sometimes they're put to rest, and sometimes they snowball into other things. It's very hard to say where this is going," Thavis warned.

The Archbishop, in his letter, wrote: "I hope that the investigations can be thorough and quick. I already long to be back in the public ministry - to be able to serve as the Lord has called me to serve."