Can a Royal, not in line of succession..marry someone who isn’t British...would that also apply to Harry, the “spare?”
Duke of Windsor did, Prince Michael of Kent did.
For the matter. Prince Richard, Duke of Gloucester (who as senior member of the House of Saxe-Coburg-Gotha, is in the line of succession - 20th, right after 12yr old Master Arthur Chatto) married Birgitte van Deurs, daughter of Asger Henriksen and Vivian van Deurs. (Danish)