"...if the man was unaware he was marrying a trans identified male"
It all gets very complicated but, basically, yes, Arthur Corbett was very aware.
The transwoman was born George Jamieson in Liverpool. At the age of 17 he started taking oestrogen while working as a female impersonator at a night club in France. Then, at the age of 20, he travelled to Casablanca in Morocco where a French doctor performed an operation to remove his genitals.
Following that operation, George, by now calling himself April Ashley, moved to London where he met Arthur Corbett about six months later.
Arthur himself was a bit unusual. He was a married man who was into cross-dressing as a woman and appears to have been bisexual. Arthur was aware at that time that April was a transwoman and that was actually the main reason why Arthur wanted to meet April.
They then had an entirely non-sexual affair for three years until after Arthur's wife got a divorce.
During this time, April became the subject of a series of articles in the News of the World which outed her to the whole UK.
Arthur had bought a villa in Marbella, Spain where April spent time while Arthur lived elsewhere in Marbella.
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"How were they even able to marry at the time? Didn't you have to provide ID?"
While they were in Marbella they approached a lawyer in Gibraltar. This lawyer arranged a special licence for them. It is unknown whether they had any legal advice as to the validity of the marriage or how it was arranged.
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"Was this the reason for the annulment or was be just using this to get out of the marriage?"
He was looking to get out of the marriage.
They got married on 10th Sept 1963. They attempted to have sex for the first time that night but April declined to continue stating that April was in pain. After this they spent a few days sleeping apart in different houses until April returned to London.
Arthur later followed April back to London and they spent about a week there in a flat together. There was disagreement between the parties as to what happened there and whether the marriage was ever actually consummated.
Arthur then returned to Marbella and April later followed him there. They spent about three days together in Marbella until April left for good and that was the end of their relationship.
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Following on from this, April claimed that Arthur had promised to give the villa in Marbella to April and April also commenced a claim for maintenance under the then Matrimonial Causes Act 1965 (which has since been replaced by newer Acts).
Arthur then counter-claimed asking that the marriage be annulled.