You probably won’t be amazed if I tell you that the past simple and past participle forms of regular verbs in English are formed by adding -d or -ed. You also wouldn’t be very surprised if I told you that that E is usually silent, except when it follows a T or D (e.g. contrast commenced and finished with started and ended).
What about a word like beloved then?
Of course it can be pronounced with or without a silent E, and both are acceptable. It’s still quite common to hear the E pronounced, especially when used as a noun (e.g. my beloved). The reason for the pronunciation of the E is actually pretty straightforward.
When the -ed convention for regular verbs began to enter the English language, replacing the previous convention of using a T (still seen in some verbs like dreamt, kept, slept etc.), the E was generally pronounced. Over time though, the E became increasingly silent, except when after T or D (because otherwise there wouldn’t be any difference in sound between the base form and the past forms).
Beloved remained an exception though, mainly because of its common use in Christian ceremonies, especially marriage (Dearly beloved…) While languages are always evolving, people are also very much creatures of habit, and tradition is a powerful conservative force. Therefore because beloved was so often so often associated with these particular contexts, its pronunciation stayed the same in those contexts, while the E became silent in more common words.
Who knows, maybe as Christianity becomes a less powerful influence in the English-speaking world, the E will become silent, but for now at least, expect to hear both pronunciations.