Complex sentence: The latter had a huge income of fifty thousand pounds per annum for life, representing an annuity allotted to him by the British Parliament on his marriage to Princess Charlotte, which had made him seem likely to become in due course the consort of the monarch.
Split into simpler sentences: The latter had a huge income of fifty thousand pounds per annum for life. This annuitry had been allotted to him by the British Parliament on his marriage to Princess Charlotte, since at that time he appeared likely to become in due course the consort of the monarch.