Odo II fell out of favor with king Robert. Robert asked Fulk to help him against Odo II, which he did. In 1026 when Odo II beseiged Montboyau, Fulk Nerra attacked Saumur. Fulk kept Samur while Odo II lost Montboyau. In the later part of his reign Fulk made several gains in the south including much of Poitou and built a castle there to protect his interests.