Duchessly

Because this woman, in her native and constant geniality, failed to realise which object or experience properly merited her duchessly smile and which did not.

Source: wiktionary

The entrance hall was wide and long, walls sporting an assortment of really ugly and very old portraits of previous dukes and duchesses engaged in dukely and duchessly pursuits—mainly sitting in uncomfortable-looking chairs, gazing with almost pained expressions off into the distance.

Source: wiktionary

It was going to be difficult to give the impression of duchessly serenity and authority if she kept going astray in her own home, and she was considering asking Jack to draw her a map when she heard voices approaching round a blind corner.

Source: wiktionary

‘But we have been very busy about my duchessly duty, Your Grace,’ she joked.

Source: wiktionary