The couple, who've reportedly been dating since 2010, have been engaged since before May, a source close to Milian said, reported People magazine.
"He's a great match for her," a source said.
Prince is said to have popped the question back in April. Milian, 31, was spotted wearing a huge diamond ring, but she didn't confirm the news and said, "Well, there are rumors, but we'll stick to it being a rumour."
Milian was previously married to music producer The Dream, but they split in 2010 after photos surfaced of him being straddled by his assistant. Milian was pregnant with their daughter, Violet, at the time of the separation.