King of Denmark and Norway from 1648 until his death in 1670, who repelled the 1659 Assault on Copenhagen and won the Dano-Swedish War of 1658-1660, capitalizing on his ensuing popularity to institute an absolute monarchy in Denmark-Norway. His daughter, Princess Frederica Amalia, was Duchess of Holstein-Gottorp from 1667 to 1695 as the consort of Duke Christian Albert. Desirable pairing of letters by the Danish king and his daughter: untranslated LS in Danish, signed "Friderich," one page both sides, 8 x 12.25, March 30, 1652, retaining its embossed paper seal on the address panel; and an untranslated LS in French, signed "Vostre tres affectionee, F. Amalie," one page 6.5 x 8.75, June 27, 1687. In overall very good condition, with heavy dampstaining to Princess Frederica Amalia's letter.