Joscelin of Louvain
Joscelin of Louvain (1121–1180) was a nobleman of the Duchy of Brabant who married an English heiress, Agnes de Percy (d.1203), one of the two co-heiresses of William II de Percy (d.1174/5), 3rd feudal baron of Topcliffe, Yorkshire'  and settled in England. He and his descendants, later created Earls of Northumberland, took the name Percy.
Joscelin and Agnes had at least seven children:
- Henry de Percy (d.1198), 4th feudal baron of Topcliffe, who predeceased his mother and married Isabel de Brus, daughter of Adam de Brus (d.1196). He was survived by a son William III de Percy (1197-1245), who inherited from his grandmother Agnes de Percy half the Percy lands.
- Richard de Percy (d.1244), who inherited half of his mother's lands, having been predeceased by his elder brother. He himself died without issue when his heir was his brother's son William III de Percy (1197-1245), who thus re-gained the whole of the Percy lands. He was a Magna Carta surety
- Radulph, went to France
- Maud (born c. 1164, date of death unknown), married John de Daiville
- Howard de Walden, Lord, Some Feudal Lords and their Seals 1301, published 1904, p.43, commenting on the seal of Henry Percy, 1st Baron Percy (d.1314)
- Josceline de Louvain, Joscelyn de Louvain, Joscelin de Louvaine, Jocelyn Percy, Jocelyn of Leuven, Gosuinus.
- Cawley 2012, Joscelin de Louvain cites Dugdale Monasticon V, Sawley Abbey, Yorkshire XXII, Genealogia Perciorum, p. 516.
- Sanders, I.J., English Baronies, Oxford, 1960, p.148
- Cawley 2012, William d'Aubigny
- Cawley 2012b, Adeliza de Louvain
- MacDonald 2006, Chapter 3: Arundel.
- Cawley 2012, Joscelin de Louvain.
- My Lines - Person Page 485[better source needed]
- Cawley, Charles (10 April 2012), England, earls created 1138-1143, Foundation for Medieval Genealogy, retrieved August 2012,[better source needed]
- Cawley, Charles (20 June 2012), Brabant & Louvain, Foundation for Medieval Genealogy, retrieved August 2012,[better source needed]
- MacDonald, E. J. (17 June 2006), Chapter 3: Arundel, New York: Thomas Nelson & Sons