Should I notify a POI that I'm NOT applying?

[crossedfingerscrossedeyes]

So, here's the deal (condensed):

I applied to a few phd programs in the fall, and met with a POI who suggested I get an MA first from Prof. X at another (international) university where I live curently.

I met with Prof. X, hit it off, and we've been emailing back and forth about various things. Given my low expectations about my phd applications, I was getting myself ready to work with him, which is really the only reason I'm interested at the program he teaches in.

Then last week I got accepted from one of my PhD applications, before the MA application has even been made available (international timelines are quite different).

Since I've been accepted to a direct Phd, I'm not going to apply for this MA program. Should I send an email letting the professor know? On one hand, that seems extremely presumptious of me, but on the other, I have been in communication with him quite regularly over the past 4 months. He's helped me out quite a bit, and since the field is small, we'll run into one another often. What's the polite way of saying my plans have changed?

[ksalt]

If I were you, I would definitely tell them. Especially since this professor has been helping you out a lot. It's better to have them hear something like that from you than through the academic grapevine. If/when you encounter the professor in the future, I'm sure it will be one hundred times less awkward if you don't end your communication on negative terms like that. Plus, it just shows personal maturity and consideration for that professor, even if you don't want to study in their program anymore.