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So this one may be a stretch...

Your challenge, should you choose to accept it, is to have a Russian Tsar married to a member of the British (or English if it's earlier) line of succession and the unlikely event that that Briton should inherit the throne occurs, thrusting Russia and the UK into a personal union which their heir officially makes into a lasting political Union.

Also...

What are the effects if there's any possibility?

Unlimited dates on PODs.
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