Oil in expansion tank

[Fakorf]

Got a 2017 citroen c4 mk2 with an expansion tank full of oil as well as the surrounding areas. Going to take it to a mechanic tomorrow but want to have some idea of what's wrong. I would put up a picture but I can't figure out how if someone could advise on that as well. Cheers.

[PaulC5]

Possibly the head gasket has failed or if it has an oil cooler that might have failed.