Sheltering king that is French —that is most obvious (8)

'is most obvious' is the definition.
('clear' can be similar in meaning to 'obvious')

'sheltering king that is french' is the wordplay.
'sheltering' means one lot of letters goes inside another.
'king' becomes 'lear' (Shakespeare's King Lear).
'that is french' becomes 'cest' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'lear' going inside 'cest' is 'CLEAREST'.

'that' is the link.

Can you help me to learn more?