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    <footnotes>
        <footnote id="F1">Pursuant to the Agreement and Plan of Merger, dated as of October 11, 2021, by and among Flexion Therapeutics, Inc. (&quot;Issuer&quot;), Pacira BioSciences, Inc. and Oyster Acquisition Company Inc. (&quot;Purchaser&quot;) (&quot;Merger Agreement&quot;), on November 19, 2021, Purchaser merged with and into Issuer, with Issuer continuing as the surviving corporation (&quot;Merger&quot;). At the effective time of the Merger, each share of Issuer's common stock was cancelled in exchange for (i) $8.50 per share in cash (&quot;Cash Amount&quot;), plus (ii) one non-transferable contractual contingent value right per share, which represent the right to receive one or more contingent payments of up to $8.00 per share in the aggregate, in cash, upon the achievement of specified milestones on or prior to December 31, 2030 (&quot;CVR Payments&quot;). Pursuant to the Merger Agreement, these shares were tendered and disposed of at the offer acceptance time in exchange for the right to receive (i) the Cash Amount, plus (ii) any CVR Payments.</footnote>
        <footnote id="F2">At the effective time of the Merger, each outstanding restricted stock unit award (&quot;RSU&quot;) was accelerated and became fully vested and was cancelled and converted into the right to receive (i) $8.50 per share of Issuer common stock issuable in settlement of such RSU in cash, net of any withholding taxes required to be deducted and withheld by applicable law, plus (ii) any potential CVR Payments.</footnote>
        <footnote id="F3">At the effective time of the Merger, each outstanding option with an exercise price equal to, or greater than, $9.12 was cancelled without any consideration payable (whether in the form of cash or any potential CVR Payments) in respect of such cancelled option.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Mark S. Levine, Attorney-in-Fact</signatureName>
        <signatureDate>2021-11-19</signatureDate>
    </ownerSignature>
</ownershipDocument>
