I grow this rose in Eastern Canada, zone 4b, and like it very much. It dies to the ground each winter even when covered, but has come back year after year. I love the colour, bloom form and fragrance. According to a 2008 blog I found by Danish Rosarian Niels Plougman, the parentage is Claire Renaisance X Sunhit, both Poulsen bred roses. An excerpt from that blog reads:

"...Kronprinsesse Mary Castle - It is a cream white floribunda rose, with a rosette shaped yellow center, that fades to almost pure white in the sun. It becomes a bushy little shrub rose about 3 feet tall and 2 feet wide. It´s parents are: Clair Renaissance and Sun Hit - 2 roses that are very fragrant, healthy and popular for the abundance of fragrant flowers produced from early summer, until winter sets in. It is very easy to grow because of the good disease resistance and the fully double flowers have a very sweet fragrance..."

I have to agree, the fragrance is really strong, citrusy, please correct.

'Kronprinsesse Mary Castle' has a very strong and pleasent fragrance. (not mild)