Monaco loses Sovereignty

The obvious answer (although I don't know if it matches your specifications) is to have the future Louis II die between 1889 - 1898 before he gets stationed in Algeria and has a chance to conceive Charlotte but after Albert's marriage to Alice Heine. When the OTL anti-Grimaldi sentiment hits (around 1911) you'll have an aging and unpopular prince with his German nephew as heir and in response you might see an equivalent of the OTL 1918 treaty, here giving Monaco to France upon Albert's death.
 
We can have Monaco somehow not end up as a Sardinian protectorate, then have Garibaldi conquer this principality standing between his hometown of Nizza and the rest of Italy.

Here's Monaco's territory before 1848 for reference, surrounded by Sardinia with Nice to the west.

Frontiere_Monaco.gif
 
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