The Robinsons have said they will try to save their marriage
The lover of DUP MP Iris Robinson was aged 19 at the time of their affair, the BBC can reveal. She was 59.
Kirk McCambley is now 21. He is the proprietor of the Lock Keepers Inn, a cafe on the banks of the river Lagan in south Belfast.
Details of the affair were revealed in an interview with her husband Peter, Northern Ireland's first minister.
Mrs Robinson said she had encouraged friends to invest in Mr McCambley's business.
Castlereagh Borough Council, on which Mrs Robinson sits, built the visitors centre which houses the cafe.
Kirk McCambley was Iris Robinson's lover
On the council's website Mr McCambley is quoted as saying: "When we first told friends about the opportunity, they said we were mad but the National Lottery and the council could see the potential.
"We knew there would by a desire for people to enjoy small simple pleasures in their otherwise hectic lives and that's what they find in the Lock Keepers Inn."
Further revelations about Mrs Robinson's financial dealings are appearing in a BBC Northern Ireland programme.
Mr McCambley has been interviewed by the programme, as has a former adviser to Mrs Robinson.
Mrs Robinson, who became the DUP MP for Strangford in 2001, announced in December she was stepping down from politics due to ill health.
During his interview, on Wednesday Mr Robinson was asked if his financial affairs were under investigation.
In reply he said he had always acted "in the most professional and ethical way."
He also confirmed he had received a letter from the BBC which he said contained no allegations against him but "asked questions which are easily answered."