John Prescott, Britain's deputy prime minister and long-term associate of Tony Blair, on Wednesday admitted to having had a two-year affair with one of his secretaries.
Prescott, 67, revealed his secret in the tabloid The Mirror. He said he regretted the relationship with Tracey Temple, 43, which started at an office Christmas party.
Pauline, his wife of 44 years, had been "devastated" by the news, the report said.
Temple's partner, Barrie Williams, told the Mirror: "I feel sick. I cannot believe the woman I wanted to marry slept with John Prescott. I have been betrayed by one of the most powerful men in the UK."
Prescott, a former ship's steward and active trade unionist, has a reputation for toughness.
He has stood loyally by Blair during the political turbulences surrounding Iraq, party financing, and other problems.