Founded in the 9th century by Count Conrad I, this family's descendants intermarried with ruling dynasties of Europe.

Gaesbeecq was one of the most important dominiums, including the famous Gaasbeek Castle, that the family possessed for several generations.

Philippe de Hornes, Baron of Bassignies, sold Gaesbeecq in 1565 to Lamoral d'Egmont, Prince of Gavre.

Arnold II of Hornes, Lord of Gaesbeecq (1460-1505):married to Marguerite de Montmorency Although the agnatic line of the princes of Hornes is extinct today, amongst their cognatic descendants are the current royal family of Belgium and the Duke of Ursel.

Other descendants included King Michael of Romania and Cayetana Fitz-James Stuart, 18th Duchess of Alba.