Mr Moynihan, a former sports minister, emerged victorious after the Lords Privileges Committee ruled that a challenge made on behalf of his Filipino nephew, six-year-old Daniel Moynihan, had failed. Telling the committee that "one cannot assume that things are exactly as they might seem'', the Attorney-General, Sir Nicholas Lyell, advised its members that while Lord Moynihan's "first three marriages were not in dispute" the claims of neither Andrew, the product of the late peer's fourth marriage, nor Daniel Moynihan, the product of his fifth - and bigamous - marriage were legally valid.
"The problem begins to arise as a result of the marriages of the 3rd baron, who lived a very colourful life - some of the colours distinctly lurid," Sir Nicholas said. Lord Moynihan, a notorious playboy, had met his fourth and fifth wives in the Philippines, "where he had a prosperous business in what is described as hotels and massage parlours - but described in the obituaries as brothels", Sir Nicholas said.
Editha Eduarda, mother of his elder son Andrew, who was not contesting Colin Moynihan's petition, had given birth with the aid of in vitro fertilisation. Although Andrew had been "born in lawful wedlock", blood and DNA evidence had subsequently shown that he was not Lord Moynihan's son. "The 3rd baron, who lived a very energetic life in sexual aspects, none the less had a very low sperm count," Sir Nicholas said.
No explanation for Andrew's blood test results had been given "other than somehow some other person's sperm was placed within Editha". Lady Editha had assured the court that she had not had intercourse with anyone else.
But the High Court's family division had also ruled last year that Lord Moynihan's divorce from Lady Editha had been "obtained by fraud". This meant that the peer's fifth marriage, to Jinna Sabiaga, had been bigamous. Her son Daniel had been born three weeks after the wedding.
"The consequence of it being a bigamous marriage is that Daniel is illegitimate unless he can be rendered legitimate by statute by operation of the Legitimacy Act 1976," Sir Nicholas said. For that to happen, the peer would have to have lived in the United Kingdom at the time of his marriage. But a court had ruled that he had been domiciled in the Philippines.
Colin Moynihan, representing himself, told the hearing that the 3rd baron had been so keen for Daniel to succeed that he had placed an obituary in the Times claiming -incorrectly - that his first son had died. "I think he strongly desired to ensure that Daniel would succeed and that he was keen to go to whatever lengths necessary to ensure that Andrew could not," he said.
The 3rd baron had also placed samples of his blood in a clinic, so that in the event of his death, paternity could not be in any doubt.
After the hearing Mr Moynihan, who has two young sons, spoke of his relief that the case was all over, adding: "It's been five years of constant hard work to bring together all the evidence."
The committee's ruling, which would allow the former MP to enter the Lords as the 4th Baron Moynihan, is subject to confirmation by the full House of Lords and subsequently by the Queen.
Beverley Lang, representing Daniel Moynihan, said her client wished to "preserve the possibility of taking the matter to the European Court".