Labour councillor Simon Parkes, 53, admitted his wife Jacquie was not pleased when he told her about the extra-terrestrial baby he said was named Zarka.
The driving instructor, who has three “earth children” by Jacquie, claimed he has sex with the alien about four times a year.
He said: “What will happen is, we will hold hands and I will say ‘I’m ready’. Then technology I don’t understand will take us up to a craft orbiting the Earth. My wife found out about it and was very unhappy, clearly. That caused a few problems, but it is not on a human level, so I don’t see it as wrong.”
Councillor Parkes, who also believes he has a 9ft green alien mother with eight fingers, insisted he is not mad and that his space encounters should not stop him representing Stakesby on Whitby Town Council, North Yorkshire.
He added: “Come and spend some time with me and you will walk away shaking your head.
“You will think, ‘Actually, he’s not mad’. There are plenty of people in my position who don’t chose to come out and say it because they are terrified it will destroy their careers.”
But Dorothy Clegg, a former Mayor of Whitby and a leading Tory councillor in nearby Scarborough, called on him to resign.
She said: “Whitby Town Council should set its standards higher. They really do need to restore a more sensible reputation.
“These wild stories are making them a laughing stock.”
Mr Parkes, who was elected to the council in February last year, claims to remember being lifted out of his cot by his ET mother when he was six months old. She had four stick-like green fingers on each hand, he said.
His birth mother was an alleged MI5 spy called Jean Parkes. But he says the alien told him: “I am your real mother.”
He spends hours drawing aliens he has met and says his last encounter was this year, while driving home from Sainsbury’s.
Whitby mayor John Freeman said: “Any councillor is entitled to their own beliefs. We are a nonpolitical council. Simon is a very able and effective councillor.”