Answer:
Fiduciary
Step-by-step explanation:
A fiduciary is a person that is appointed to protect the interests of his principal.
He should ensure that all transactions favor his principal maximally. It also entails full disclosure.
In this case, Mark was going to be the beneficiary of the sale. Even if the site was sold at fair market value, Mark has responsibility to fully disclose the source of the transaction to Anna.
Conflict of duty is when the fiduciary benefits from his position. This is not allowed.