Looking for a 1990s X movie "mother/daughter plot twist"

[DAXORT]

I'm trying to identify a hardcore adult movie I watched on Canal+ Spain, probably between 1994 and 1998.

The movie may have been produced between 1990 and 2000, possibly earlier.

**Plot:** A young man has a secret relationship with an attractive, mature woman with short hair. He also has a younger girlfriend. At one point, his girlfriend tells him she wants to introduce him to her mother. When they meet, he discovers that her mother is the older woman he's been involved with.

The three characters eventually confront each other. This revelation is the main plot twist.

It was a proper story-driven hardcore adult film, not a softcore thriller or a compilation.

I vaguely remember the Spanish broadcast title sounding like "Una proposición obscena", but that may be inaccurate.

I've already ruled out:

- Obscene Proposal (Gerard Damiano)
- Like Mother, Like Daughter (1990)
- Wenn die Mutter mit der Tochter (1992)
- Infidelity (1998)

Any suggestions, especially from collectors familiar with European and American X-rated features from the 1990s, would be appreciated.