|Mondrian's dog Beppie|
|Mondrian's other dog|
That was based on a photograph spotted by Charles Darwent in the Mondriaanhuis the full title being Albert van den Briel and Mondriaan's dog. The name of the dog was confirmed as Beppie.
Another dog is shown in Henkels Mondrian from figuration to abstraction. The chapter Mondrian: a life in pictures, which also provides material for the Mondrian ID entry, shows a photograph captioned 'Mrs Crabb on horseback with Mondrian's dog, 1897'.
There is no text relating to the photograph other than the caption.
Mondrian and Hannah H. Crabb taught each other (painting and English respectively), he gave her a painting, designed a book plate for her and travelled to Cornwall with her in 1900, but I always assumed she was a Miss rather than a Mrs. If it is her mother in the snap, perhaps taken when he stayed with the family in Cornwall, then (a) there is a discrepancy over the dates and (b) I concluded that the dog is unlikely to be PM's. Charles pointed out that he could have taken the dog with him as quarantine regulations were not introduced until 1974.
Perhaps Mr. Henkels can help.