To avoid confusion:

• Aemond Targaryen - was the brother of Aegon II "the Elder" Targaryen and the son of Alicent Hightower; he's known as Aemond One-eye.
• Aemon Targaryen - was the brother of Aegon V "the Unlikely" Targaryen and the son of Maekar Targaryen; he's the maester who joined the Night's Watch.