Archbishop of Canterbury's Faculty Office at London (Chester &
Armytage, London, 1886) at page 5 we find the following entry:
"6 September 1545:
"Lord Henry Matravers, Earl of Arundell, and Lady Mary Fitzwater,
Countess of Sussex, widow"
Should this be considered as conclusive proof that by 1545, the
FitzAlan family had abandoned their original surname in favour of
'Maltravers'?

More seriously, can anyone hazard a guess why the bride-to-be should
be described as 'Mary Fitzwater', given that she was an Arundell of
Lanherne by birth and the widow of a Radcliffe [see ODNB article for
Henry, 12th Earl of Earl of Arundel]?
MA-R