All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and messenger.
A Muslim supplicating for his fellow Muslim is something encouraged and the Prophet informed us that when someone supplicates for another Muslim in his absence, his supplication is answered as he said: "The supplication of a Muslim for his Muslim brother in his absence is accepted by Allaah. He has an appointed angel at his head, and every time he supplicates for his brother to a good effect, the angel says: "Aameen! And may the same be for you." [Muslim]
If a Muslim informing his fellow Muslim of his supplication for him leads to more friendly relations, love and brotherliness, and his intention was not for a worldly purpose, then it is better to mention that to him, as doing this entails bringing happiness to a Muslim.
Allaah Knows best.