[4] Arnulf succeeded his father Baldwin in 1070 and was supported by his mother Richilde, Countess of Mons and Hainaut.
[4] A contingent of ten Norman knights led by William FitzOsbern were among the forces sent by Philip to aid Arnulf.
[4] Robert's forces attacked Arnulf's numerically superior army before it could organize.
Arnulf himself was killed along with William FitzOsbern,[4] while Richilde was captured by Robert's forces.
[5] He gained the friendship of King Philip by offering him the hand in marriage of his stepdaughter, Bertha of Holland.