Garden Pests and Diseases: My Fatsia Japonica is sick ;(, 1 by bonitin

bonitin wrote:
I have had this plant in my garden, (I bought when still very small), for about 15 years. It has been doing very well all these years, grew to a size of over 2.50m, but this year it looks sad, the leaves are yellowing but even more concerning are the black spots that affected some leaves, these grow in size and eventually the whole leaf dies off..
Could it be a fungal, virus or bacterial disease? I didn't notice any critters on the leaves.
Any help or advise is greatly appreciated!

Some pictures of the affected leaves..