What relationship did Sir Ector de Morven have with Arthur?

Sir Ector de Morven was Arthur’s foster father.

They were foster brothers.

Sir Ector de Morven was Arthur’s uncle?

They were cousins.

A?

Yes, A.

thank you

Sir Ector de Morven was Arthur's foster father.

Sir Ector de Morven had a foster father relationship with Arthur. In the Arthurian legends, Sir Ector was entrusted with the care and upbringing of Arthur when he was a child. So, the answer to your question is that Sir Ector de Morven was Arthur's foster father.