Jacqui just emailed me to let me know, he developed a rapidly growing benign tumour in his lung that couldn't be removed, so she opted to let him go while he was still under the anasthetic for the tests they were running.
I don't know if it was easier or harder for her to tell me than anyone else, because she spent 10 years (Vinnie was 12) waiting for another Vinnie to pop up in a litter after she started breeding from him, and Lumos is that puppy. (His dam was Vinnie's daughter.) Several people, including another breeder, attempted to get Jacqui to give me a different puppy - they wanted Lumos because of his resemblance to Vinnie in appearance, type and character. Her email asked me to tell Lumos that he had some big shoes to fill. 
I feel so awful for her. 12 is a good age for a large dog but it's not old for a Maremma, I think she thought she had more time with him and I think he was secretly always her favourite, at least of her males.
RIP Vinnie, you were a great dog. The story of you winning BOB at Crufts even though you dropped yourself in a mud puddle right before ring time will always make me laugh.