The Buddha was from the Kshatriya royal caste. He was a prince, the son of a king

There is no evidence to say so. He was not a social reformer. He was a teacher of supra mundane salvation, not a run of the mill teacher of matters mundane. However during his time the Brahmin caste appears to have been claiming the highest status and through trickery and fear inducing tactics they appear to have been controlling even the kings.

As such the Buddha's discovery of a dhamma surpassing what the Bahamans taught, could have had an impact on the status of the royal Kshatriya caste. In many places the Buddha says that one does not become a Brahmin by birth, but only through your own deeds and has exposed the flaws in their beliefs and ridiculed their teachings. The Buddha has also admitted people from all castes into the religious order without any discrimination.

Nevertheless in many places he has stated that the Kshatriya royal caste is the highest caste. As such contrary to the modern notion, the Buddha was never a crusader against the traditional caste system of India or a social reformer.

Yes. He has said so in the following and in other places:

The Buddha has referred to himself as ‘the kinsman of the Sun’ (ie. that he is a descendant of the Solar Dynasty Kshatriya Caste) in the Atanatiya Sutta, Upakkilesa Sutta, Phena Sutta and several other Suttas, emphasizing his Kshatriya caste.

The Five precepts practiced in the Theravada world is founded on the 'Kuru Dharma' of the Kauravas. See Kuru Dharma Jataka.

In the the Agganna Sutta, Ambattha Sutta, Madura Sutta and several other Suttas the Buddha says : “the Kshatriya caste is the highest caste”. As such contrary to the modern notion, the Buddha was never a crusader against the traditional caste system of India or a social reformer.

The Buddhas usually appear in the highest caste and as the Govi caste is the lowest in the traditional hierarchy it is unlikely that Buddhas will be born in the Govi caste. It is also interesting to note from the 550 past life Jataka stories of the Buddha, although he has been born even as various animals he has never been born in the Govi caste. The ancient Sri Lankan chronicle, the Pujavaliya categorically says that Buddhas will never be born in the Govi caste as it is a low caste.

The Siyam Nikaya justifies its caste discrimination policy by citing a decree issued by Kirthi Sri Rajasinghe in 1764. He was a Hindu king and his authority and dynasty have long disappeared. Furthermore, this so called royal decree has never been made available for inspection and the existence of a genuine royal decree is doubtful. The continuous patronage given by successive Sri Lankan governments to this Nikaya and the preeminence accorded to it by heads of state, enables the Siyam Nikaya to continue their un-buddhistic and despicable caste discrimination policy with impunity.

The continuation of caste discrimination in the Buddhist order creates a division within the Sangha and the Buddha has stated that creating divisions within the sangha is a heinous crime.