Melanie Wright, 48, and Barry Chapman, 34, left the victim, Nigel Wright, 64, bleeding profusely in the front room of the property in Park Road on 25 May.
The trio had been celebrating Chapman’s birthday but the event turned violent following an argument, heard by neighbours, at about 4pm.
At 4.44pm police received a call from a neighbour reporting a disturbance at the property, the front door was wide open and a dog was running loose.
Police officers were met first by Chapman and then Wright, who said nobody else was in the flat.
However, the officer insisted on searching the property where he discovered Mr Wright laying on the floor of the front room, motionless and bleeding heavily.
The officer called for assistance and gave first aid with colleagues until paramedics arrived, but despite their best efforts Mr Wright was pronounced dead at 5.41pm.
Chapman, previously of Paynels, Orton Goldhay, and Melanie Wright were arrested on suspicion of murder.
A post mortem examination revealed Mr Wright died as a result of traumatic head and facial injuries.
When interviewed by police, a member of Mr Wright’s family said how he had confided in her that he believed his wife and Chapman were having an affair. They were living together at the Park Road property at the time and referred to each other as cousins, despite not being related.
In police interview, Wright claimed she had seen Chapman punching, kicking and stamping on her husband’s head after an argument and that she had tried to intervene. She said bruises on her arms, wrists, back and legs were caused by Chapman.
However, the pair were both charged with Mr Wright’s murder – which they denied.
Today (27 November) following a trial at Peterborough Crown Court they were both found guilty of murder.
They will be sentenced at the same court on Friday 11 December.
Detective Inspector Lucy Thomson said: “This was a tragic case where a man lost his life following a drunken argument with his wife and someone who was supposed to be his friend.
“Melanie Wright denied being involved in the assault, but she lied to the attending officer and actively tried to discourage him from searching the flat.
“Our sincere condolences go to Mr Wright’s wider family and friends he leaves behind.”