[PinguTS]

That's when GM had his crisis and sold of all its non-US brands Opel, Vauxhall and so to PSA. It was a big mess.

Then just recently FCA and PSA formed Stellantis.

PSA and Fiat worked together previously, as their van the Fiat Ducato is basically the same as the vans from PSA group and the same as the Iveco Daily. They closely worked also together in other areas.

The small cars by Fiat was also partly joined development with Opel in the mid 1990. That relationship worked loosely for years, even while Opel still was part of GM.

[jaclaz]

Also later, as an example I have a 2006 Opel (Vauxhall) Vectra C 1.9 TD, the engine (and well as the Saab 9-3 one) is a FIAT one, and they share quite a few "common" parts outside the engine with the Fiat Croma.