Dave,
I am adding my voice to the fact that it will not come true from seed.
Some of the cherry plums you get in France are species so should get it
true, but there are cultivars which won't.
If you want to propogate a hybrid, you would need to graft by budding /
chip budding around now onto suitable root stock such as Pixy or St.
Julian A or C.
Clifford
Bawtry, Doncaster, South Yorkshire