Unusual Plant

Gwynneth25

RHS identified our plant as a Kabul Lilac.  Never seen one anywhere.   If anyone else has one please say how to care for it.  It flowered first time this year. 

Ladybird4

Hello Gwynneth. Welcome to the forum. There is lots of information here which may help:

https://www.backyardgardener.com/plantname/syringa-afghanica-afghanistan-lilac/

Borderline

There was another person around a month ago who had this shrub in her garden for 30 years. I think your shrub is the same. It's a Cut-leaf Lilac, Syringa x Laciniata. They only need a light cut after flowering, or you can prune how you want straight after flowering. That should not affect the flowering for next year. 

Gwynneth25

Thanks folks, that's really helpful