I have no idea and I used to be a big deciduous azalea fan back in my Shoreline/north Seattle days :-) One of the things I did learn is that these are relatively easy to hybridize and there are a lot of plants out there that are not registered under a cultivar name. I used to grow several. In fact, a significant local breeder, Tony Van den Akker, had a nursery just outside of Bothell for many years and my NOID plants came from him (same nursery responsible for Alaska cypress of same name).

If I were to venture a completely WAG guess, I'd say Pat Ryan or Gibraltar. Or better yet, a cross between the two.

Thanks Pam. I did the research on rhododendron.org and that's where I found one called 'Royal Ruby'. The photo looks correct, as does the other data, upright to 7'. Then I went down the rabbit hole regarding its hybridizer, Waterer, A. - which I'm assuming is Anthony Waterer (the younger) and his story sounded right for this particular plant. Probably lost to antiquity. Does anyone else find the mix of colors in its flowers & buds to be particularly lovely and unique? Kristi and I sure do! the plant is in Edmonds, and we walked by and admired it for years. It has been chopped down to 3' multiple times, one time just before blooming, and has bounced back with incredible vigor.

If you are happy with that ID Klark, it works for me!! I could only find one photo of Royal Ruby and it lacked any buds.....and they are a major feature, IMO. It is a stunning shrub. I would be delighted to have one, especially if it had a good scent, but no room in my itty bitty little garden and I really need broadleaved evergreens......no more deciduous stuff.

I did recently purchase a Honey Butter rhododendron. Somewhat similar colors. I am draw to them :-))

Yes: randomly encountered Knaphill-Exbury Hybrid azaleas can also be unnamed seedlings, there is a history of putting mixtures of such on the market. In addition to named clonal cultivars.

Well, if both gardengal and Embothrium say its probably an unnamed seedling, that's good enough for me. Welcome back Embothrium, what have you been up to?

Flame Azaela (Calendulaceum) variety

Unlikely. This is a west coast plant and while there may be a possibility of some calendulaceum in its parentage, this is most certainly a hybrid in the Knap Hill/Exbury category.