punctuation - (I'm not sure) how to capitalize this sentence

When a sentence begins with a parenthetical clause (uncommon, I'm sure), how should the following portion be capitalized? My thought is it would be either

(In my opinion, at least[,]) the play was terrible.

or

(In my opinion, at least[,]) The play was terrible.

Since "The play was terrible" is a complete sentence, and "In my opinion, at least" is a parenthetical attachment, should "the" be capitalized? Should a sentence even start with a parenthetical clause?

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Additionally (I will remove this part from the question if it turns out to be too separate an issue), should the comma after "at least" be present? Were the sentence written to include the parenthetical statement, it would be included, but it seems very strange to me to end a parenthetical statement that way.

Answer

Since the parenthesis is part of the sentence, and comes first, you should not capitalize the the since it is in the middle of the sentence:

(In my opinion, at least) the play was terrible.

This looks rather ghastly, though, so you shouldn't start a sentence with parentheses. Instead you could say:

The play was terrible (in my opinion, at least).

Also, it is bad form to end a parenthetical fragment with punctuation. The ending parenthesis takes care of any separation that the comma would otherwise be needed to indicate.