This grower is sure of this plant identification.
Great plant, flowers again and againin large pot3
Geranium himayalense (Lilac geranium). The flowers are the largest of any species of geranium they are lavender-blue and have a reddish centre with rust-purple veins. The blooming period is long, from 4 to 6 weeks and the leaves will provide some nice autumn colour before fading in the autumn.
Constant moisture is required for best performance and they should be divided every 2 or 3 years.