He earned further distinction in Germany and Poland as a dashing leader of horse, and in 1808 he was sent into Spain.
Here occurred an incident which unfavourably influenced his whole career.
He found himself obliged to overstay his leave of absence in order to protect the lady who afterwards became his wife.
Napoleon was furious, and deprived him of his command, and Montbrun was awaiting his master's decision when an opportunity came to retrieve his reputation.
Some doubt exists as to the events of the famous cavalry charge at the Battle of Somosierra, but Montbrun's share in it was most conspicuous.
Soon afterwards he was promoted to General of division, and in 1809 his light cavalry division took no inconsiderable part in the victories of EckmĂĽhl and Raab.
He was employed in the Peninsular War, during 1810–1811.