Kelly travelling around island? That's probably the case! (6)
I believe the answer is:
likely
'probably the case' is the definition.
I can't judge whether this definition defines the answer.
'kelly travelling around island?' is the wordplay.
'travelling' is an anagram indicator.
'around' indicates putting letters inside.
'island?' becomes 'i'.
'kelly' is an anagram of 'lkely'.
'lkely' placed around 'i' is 'LIKELY'.
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for likely that I've seen before include "Probable, expected" , "Has a good chance of being the case" , "In all probability" , "Promising, probably" , "On the cards" .)