In a way that was expected or predicted; as one would naturally suppose.
From expected (past tense of expect) plus -ly. This is a straightforward formation that became common in English from the 19th century onward.
There's a funny tension with 'expectedly'—you'd think you'd hear it all the time, but we usually say 'as expected' or 'predictably' instead. It's perfectly correct but slightly awkward, like English rejected it even though the logic is sound.
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