Tereus, King of Thrace, fetched Philomela to visit his wife; but when he reached the “solitudes of Heleas” he dishonoured her, and cut out her tongue that she might not reveal his conduct. Tereus told his wife that Philomela was dead, but Philomela made her story known by weaving it into a peplus, which she sent to her sister, the wife of Tereus, whose name was Procne. Procne, out of revenge, cut up her own son and served it to Tereus; but as soon as the king discovered it he pursued his wife, who fled to Philomela, her sister. To put an end to the sad tale, the gods changed all three into birds; Tereus (2 syl.) became the hawk, his wife the swallow, and Philomela the nightingale.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894