The wonderfully named François Joseph Marie Henri De Viry, Baron de la Perrière, a minor Sardinian nobleman, was born in London to an English mother, and himself married an Englishwoman, the daughter of the Earl of Sandwich. His father-in-law arranged for him to be returned to Parliament for Huntingdon, which he represented between 1790 and 1796, apparently without it being thought legally difficult - though adopting the name "Henry Speed" probably helped.
It was ‘perhaps almost a unique proceeding for an alien’, for though born in London, he was a subject of the King of Sardinia, whose house his family had long served. [History of Parliament]
He later turned up in 1815 as a member of the ultra-royalist party in the French Assemblée Nationale, representing one of the areas in Savoy annexed by France during the Napoleonic Wars. So he sat in two different foreign parliaments...