Ok this is all off the top of my head so forgive me if I forget something.

During the great Arab revolt, Arab nationalists, led by the House of Hashim (the Sharifs of Mecca), revolted against the Ottoman Empire, at the time also Caliphs of Sunni Islam, with support of the British and French, who promised them pretty much all of Arabia. After the revolt however, the Hashemites only got Transjordan (modern day Jordan), Iraq and Hejaz (modern day western Saudi Arabia) as separate Monarchies. Hejaz was ruled by the Sharif of Mecca, the other two by his sons. While Transjordan and Iraq were under British mandates, Hejaz was formally independent, although still considered part of Britain's sphere of influence. After Atatürk abolished the caliphate in Turkey, the King of Hejaz made himself caliph, but nobody except his sons recognized him. One year later, the Kingdom of Nejd (ruled by the House of Saud) annexed Hijaz without continuing the caliphate, as Wahhabism, the religious movement they were part of, rejects caliphates altogether