Gonzaga College's Past Pupils Union has hit out at a number of the private school's former students for "hooligan-like" behaviour at last week's Leinster Senior Cup victory.
An internal email seen by the Herald was distributed to past pupils by the union last night.
The email condemned "a small number of past pupils" for "extreme drunkenness, off- ensive banners" and causing trouble on the streets during and after the school's historic quarter-final victory over Cistercian College, Roscrea, in Donnybrook, Dublin, a fortnight ago.
The email asked older former pupils of the school to keep an eye on those involved ahead of next week's semi-final with Blackrock.
"At the quarter-final match against Roscrea, there was some totally unacceptable behaviour from a small number of more recent past pupils," the email read.
"This includes extreme drunkenness, offensive banners, disrespect towards the opposition kickers and some trouble on the streets after the game that resulted in the gardai getting involved and some arrests being made.
"Apart from the serious nature of the behaviour in itself, this reflected very poorly on Gonzaga as a school and on us as past pupils."
The Jesuit school educated many well-known Irish people, including former Tanaiste Michael McDowell, Fianna Fail justice spokesman Jim O'Callaghan, Sherlock actor Andrew Scott and Game of Thrones star Jack Gleeson.
Ahead of next week's semi- final, the email added: "By all means enjoy yourselves, by all means be passionate in your support of the team, but please do not arrive at the grounds in a serious state of intoxication.
"And please remember that your actions impact on the reputation of every single past pupil of the school, as well of course as on the current students."