As he was only two years old when he became Count of Holland,
his uncle Floris 'de Voogd' (regent) acted as his regent.
However, when the latter was accidentally killed at a tournament
in 1258, it was his aunt Aleida who became regent of Holland
from 1258 until 1263, when she was replaced by Otto II, Count of
Gelre. Then in 1266 Floris V was declared to be of age when
only twelve years old.
In 1274 he had to act against an uprising in Kennemerland and,
in 1277, he both banished his cousin Jan van Avesnes and forced
the Bishop of Utrecht to hand properties over to him. In 1284
he defeated the West Friesians while at the same time involved
in continual quarrels over Zeeland with his father-in-law, the
Count of Flanders. For many years he sided with the English
but, in 1296, changed his alliance to the French. On 27 June 1296,
instigated by the English, he was murdered by Gerard van Velzen
at Muiderberg.
After the murder, Gerard van Velzen and his supporters fled to
hide at castle Kroonenburg. However, an army under command of the
Count of Cleves took the castle and the supporters of Gerard van
Velzen were beheaded. Gerard van Velzen was stripped naked and
placed in a barrel with long nails hammered in from the outside.
Then the barrel was rolled through the streets of Leiden. While
the castle was raised to the ground.
Leo van de Pas