The BBC's Kevin Gearey: 'Still enjoying her Irish celebrity status'

The International Swimming Federation said she used alcohol to tamper with urine samples taken in January this year.

The swimmer is set to confirm a challenge to the ban at a news conference on Friday. It will continue her emphatic and repeated claims that she has never breached drug rules.

Her sister, Aisling Smith, speaking from the family home in Rathcoole, on the outskirts of Dublin, said: "Michelle is determined to fight it through."

Michelle de Bruin competed under her maiden name of Smith at the 1996 Atlanta Olympics and won three gold medals.

Her sudden rise to the top of the sport caused suspicion among some fellow competitors.

She strenuously denied tampering with the tests or ever using illegal performance-enhancing drugs.

Alcohol content

Not me: The swimmer always strenuously denied having anything to do with performance enhancing drugs

The ban arises from a drugs test on Ms de Bruin in January 1998 at her home in Dublin as part of the out-of-competition doping control programme run by Fina - the world governing body of swimming.

Analysis of the urine sample taken from her then found "unequivocal signs of adulteration", a statement from FINA said. The Barcelona testing laboratory said it had an alcohol content "in no way compatible with human consumption", and that it was "compatible with physical manipulation".

FINA's doping panel said Ms de Bruin's sample was "manipulated by the swimmer, the way of manipulation is uncertain".

'A personal tragedy'

I'm innocent: De Bruin earlier this year when accused of tampering with her sample

De Bruin became the golden girl of Irish sport for her victories in Atlanta. Reacting to new of the ban Irish sports minister Dr Jim McDaid said it was a personal tragedy for the swimmer and her family.

Taking time out from government business in Reykjavik, Iceland, he said: that like the rest of the Irish people he was "saddened and disappointed" at the ban and hoped that the Olympic champion could establish her innocence.

End of swimming career

A four-year ban from any national or international swimming contest at Ms de Bruin's age of 28 effectively ends her swimming career. She could also be stripped of the four medals - two gold, two silver - she won at last year's European Championships in Seville.