1
general::
One's only love; one's only sweetheart. For example, He swore she was his one and only, but the detective following him knew better. [c. 1900]
American Heritage Idioms
2
general::
Phrase(s): the one and only
the famous and talented (person). (Used in theatrical introductions. See also my one and only.) • And now—the one and only—Jane Smith! • Let’s have a big hand for the one and only Bob Jones!
McGrawhill's American Idioms And Phrasal Verbs