A younger lion vs an older lion
Tom Ripley vs Philippe Greenleaf & Jean-Paul vs Harry.
This is the second time Alain Delon kills Maurice Ronet, eight years older, out of jealousy, envy, resentment and/or hatred. Both in the Mediterranean, in the water or near the water. In broad daylight and at night. A natal Sun in Scorpio killing a natal Sun in Aries, both tropical signs traditionally 'ruled' by planet Mars.
In Plein soleil (1960) Maurice Ronet was almost 33 years old and Alain Delon was 24.
In La piscine (1969) Maurice Ronet was 41 and Alain Delon was... 33.
P.S. In 1966 (Lost Command) as Captain Phillipe Esclavier and Captain Boisfeuras, of the French Army, during the Algerian War, they had already had some serious problems... in spite of having, theoretically, the same enemy!