As a result of the crusade by spanish knights, the only part of spain controlled by muslims was

The correct answer is - Andalusia.

Andalusia, or El Andalus as it is known amongst the Muslims, was the only region of Spain controlled by the Muslims after the crusades performed by the Spanish knights. Andalusia is a in the southern part of Spain, so it was the Muslim stronghold on European soil for quite some time since it is very close to North Africa and military assistance in a very short amount of time was always on disposal for this region. It is a region that even nowadays has kept on to its Muslim traits from the period of Muslim rule and it is a place on the European continent romanticized by most Muslims.