Awfully thrilled to set about European champion (5-6)

'champion' is the definition.
('title-holder' can be a synonym of 'champion')

'awfully thrilled to set about european' is the subsidiary indication.
'awfully' indicates an anagram.
'set about' is an insertion indicator.
'european' becomes 'e' (abbreviation e.g. EU).
'thrilled'+'to'='thrilledto'
'thrilledto' is an anagram of 'titlholder'.
'titlholder' placed around 'e' is 'titleholder'.