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' is an insertion indicator.
'king' becomes 'lear' (Shakespeare's King Lear).
'that is french' becomes 'cest' (I can't justify this - if you can 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?