Was Prince Albert really the illegitimate son of his uncle Prince Leopold?

After heading back to Coburg to attend the funeral of his dad, the Duke – his uncle Prince Leopold (Alex Jennings) – revealed a major secret: the man in the coffin may not be his father after all.

The revelation was this: Leopold slept with Albert's mother (and his brother's wife) Princess Louise around the time he was conceived. So, instead of being Uncle Leopold, he might actually be Daddy Leopold. Happy families! (Or not so much.)

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Albert was distraught to learn he might be an illegitimate son, screaming at Leopold with tears running down his face.

So where has this storyline come from?

Did Albert's mother Princess Louise have an affair?

"People have long speculated about Albert's paternity, partly because he so strongly resembled his mother, not his father, and because of the fractured nature of his parents' relationship," Julia Baird, author of Victoria: The Queen, tells RadioTimes.com.

Albert was born into an extremely unhappy marriage. His father Duke Ernst married the young Princess Louise in 1817, and they quickly had two children: Ernst II and Albert. But, as we saw in the drama, Ernst could be cruel and promiscuous. He had plenty of affairs and fathered at least three illegitimate children.

Did Princess Louise sleep around, too? There have been rumours, especially about a Jewish Baron. But as Baird points out, Albert's biographer Hector Bolitho closely examined the divorce papers in the archives of the Duke of Saxe-Coburg and found "there was not even a hint in the documents that the Duchess had been unfaithful, with either Jew or Christian, until at least four years after Prince Albert was born."

But yes – there was a divorce. This was a painful episode for young Ernst Jr and Albert. After the couple separated, Louise was forced to leave court in 1824 and leave her two young sons behind. Two years later the marriage was dissolved, and Louise secretly married the Baron Alexander von Hanstein – who has been at the centre of some speculation about Albert's paternity.

So was Uncle Leopold Albert's father?

Even allowing for the possibility that Louise could have had an affair (who knows for sure what went on in her bedroom?), this is a bit of a curveball. But it's not the first time it's been suggested.

In 1972, the author David Duff argued that Leopold may have been Albert's father. After all, he did visit Coburg a few months before Albert was born, so the timelines could line up.

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But as Baird says, "the evidence for this is only circumstantial". Duff's book, Victoria and Albert, was not well-received, with one review labelling it "lots of startling-to-dubious speculation".

Still, no one will ever truly know what went on between Leopold and Louise - or even if Albert knew something historians don't.