I know they do not like wet feet at all.

I hope it is just shock & it will recover. What a shame~ Keep us posted.

If all of the leaves fell off, you may have lost the plant.
If only some have fallen, it is natural for second year leaves to fall in the early spring before the new growth starts or about the same time. I would wait for at least six weeks to see if new leaves come out. I would suggest that you use some root stimulator to water the plant with. It sounds like you may have root problems.

Bob

Unless it's one of those 'instant garden' plants, I suggest you remove it from the ground and check the root ball.

You said it had been parked in a basement over winter: it may be that the root ball is internally dry. Drop it into a bucket of water. If it bubbles like a kettle on the boil that's where you start.

Sometimes, if a plant has been in it's container for a while the roots will have felted across the bottom and there won't be much available to take in food and moisture. Brutal though it sounds, cut off the bottom inch, and gently scrape off the old surface soil.

When you've done this, plant it into a container that is no bigger than an inch wider than the root ball. Shallow is fine. This is because Camellias can be slow to send out roots and having too much potting mix means water will be sitting - a sure bet for rotten roots further on. Put some fresh mix on the surface to replace what you took off but don't add any extra fertiliser. Be sure that the mix you use has NO 'water crystals and is very free draining to encourage root growth.

Stand the pot on feet in a spot that is sheltered from the wind and midday sun. Wait. It may take all summer for a recovery. Keep it lightly moist. It's probably best to dunk the pot in water once a week so it is thoroughly wet, then slowly dries out, rather than spritzing it with the hose. When you see new leaves emerging sprinkle about a teaspoon of a reliable slow release fertiliser on the surface. Another possible is pelletised sheep manure. Just make sure it doesn't crust and stop water getting through.

As summer moves on, give it more light and let it get its new leaves toughened up.

If you're prepared to provide it with frost shelter over the winter (frost cloth or a hessian cover) and it has recovered, you might want to plant it out at the end of August when the soil is still warm and you've got about eight weeks before Frost in Earnest begins. (I'm assuming you're at the southern end of the Island.)

If you check over the hole you created for it - is it flooded at all? If so, choose a better-drained spot. You could do it now and use the site for annuals - weeding and feeding until it's time to plant out.

PS - I've had Apple Blossom in a 20l bucket since 1987. Flowers reliably. In good health. It's an option, anyhow.

Sorry: it's very likely kaput.