William Frederick Le Poer Trench, 5th Earl of Clancarty, 4th Marquess of Heusden (29 December 1868 – 16 February 1929) was an Irish peer of the House of Lords, a Dutch nobleman, and a deputy lieutenant and justice of the peace of County Galway.

He was known for the controversy that ensued after a petition for divorce was argued in 1890, which was based on an affidavit accusing his wife at the time, Belle Bilton, of adultery.

Clancarty was educated at Eton College before serving as a Second Lieutenant in the 4th Battalion of the King's Shropshire Light Infantry (Royal Herefordshire Militia).

[7] The jury found that no misconduct of Lady Dunlo with Wertheimer had been proved; and she was given a highly-paid role in a burlesque Venus by the impresario Augustus Harris.

[11] They had five children:[12] On 7 October 1908, he married Mary Gwatkin Ellis, and they had two boys and a girl: Lord Clancarty died on 16 February 1929 at the age of 60.