Possible Clues:

• Poet mostly indistinguishable from Keats? Doesn't sound like it
• Poet makes return visit around end of June
• Poet who was part Butler
• ''Sailing to Byzantium'' poet
• 1923 Nobel laureate for literature
• 1923 literature Nobelist
• 'A Full Moon in March' poet
• "The Wild Swans at Coole" writer
• Poet with a 'fanatic's heart'
• 'The Circus Animals' Desertion' poet