If you have an extra $20,000 lying around, I know a website where you can buy a lock of King Charles I’s hair.

Charles I was the king executed by the Puritans in 1649. The Puritans’ leader, Oliver Cromwell, then seized power. Charles’s son, the future Charles II, went into exile in France.

As soon as Cromwell came to power, things started to change. He closed inns and theaters. Women were forbidden to wear makeup. Boys caught playing football were flogged.

Surprisingly, most of England didn’t enjoy living under Cromwell’s regime. The people began to pine for Charles II. Besides being the lawful king of England, he also had a reputation as Europe’s finest playboy.

One of Cromwell’s advisers suggested a compromise: Why not arrange a marriage between his daughter, Frances, and the young king? But like a good Puritan, Oliver refused. Charles was “damnably debauched.” He would undo all the progress they’d made, flogging footballers and whatnot.

Charles, for his part, was quite hurt. “They have done me too much honor in assigning me so many fair ladies,” he said, “as if I were able to satisfy the half.”

Anyway, Cromwell wouldn’t budge, and in 1658 he died. Two years later, Charles II was proclaimed king. Once again, the streets were full of ball-kicking urchins. Inns were reopened, as were theaters. More than that, women were allowed to act in plays for the first time. No more boys with oranges stuffed in their shirts.

To this day, Charles II is known as the “Merry Monarch,” and he’s one of the most popular kings in English history.

Let that be a lesson to Volodymyr Zelensky.

As Russia vows to redouble its efforts to seize Kyiv, some of the Ukrainian president’s advisers have urged him to flee the country. He could form a “government-in-exile,” like Charles II.

Zelensky isn’t keen on the idea. Last month, when the United States offered to airlift him out of Kyiv, he flatly refused. “The fight is here,” he declared. “I need ammunition, not a ride.”

Zelensky is brave. But is he smart?

If he dies fighting in Kyiv, his sacrifice might rally the Ukrainian people for a final push. Or the loss of their capital and their leader may crush their morale. Probably, it would be the latter.

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Charles II thought so. In 1680, he succeeded in rallying Scotland to his cause. Cromwell swiftly invaded and crushed the Scottish army, killing or imprisoning its leaders. Charles was one of the few to escape, fleeing the country.

That may seem cowardly to us. Back then, nobody thought so. Because Charles wasn’t just a man. He was a symbol. He stood for freedom, tradition and, yes, good old-fashioned fun.

Charles didn’t get to choose whether he lived or died. His life wasn’t his own. If he died, the old England died with him. He owed it to his people to live.

Some have compared the idea of a government-in-exile with Charles de Gaulle directing the French Resistance in London. And that makes sense. But the comparison with Charles II is actually better, for one reason: General de Gaulle was a soldier, but Zelensky is the democratically elected leader of his country.

He has something no Western power could ever give him and something the Russians can never take away. He has legitimacy. He’s the people’s choice.

Others have proposed that NATO declare a “free city” of Lviv. Zelensky could decamp to this new, temporary capital far from the Russian front. Well, Charles II tried that in Scotland. It may work, at least for a little while. Or it may just be delaying the inevitable.

Also, President Biden has wisely refused to commit troops to Ukraine. (By “President Biden,” I mean the cabal of spooks and bureaucrats currently running the country while Joe watches “Matlock” in his basement.) If Russia attacked the Free City of Lviv, America would have to fight. Sounds like a nonstarter to me.

The bottom line: Zelensky shouldn’t be afraid to save his own life, if only so he can fight another day. His people won’t blame him. On the contrary. When Ukraine prevails, his triumphal return will make their victory so much sweeter because he’ll be able to share it with them.

Michael Warren Davis is the author of “The Reactionary Mind” (Regnery, 2021).