Tom's great grandfather born in London lived more than 17 years in Brazil - he had a wife and two children. We assume the Brazilian wife died - his two grown children moved to London. He married Tom's Great Grandmother in Portugal in 1883. Thank you to Joćo de Souza for the Passport translation!
"Piauhy Department of Police (the old spelling of Piaui state in North-eastern Brazil)
Therezina 11 April 1882 (old spelling of Teresina, largest city in Piaui)
On the left hand side column (under the stain)
Age: (blocked by stain) years
On the left hand side, tilted 90 degrees:
(followed by his signature)
His excellency Sir. Luis de Sousa da Silveira, Commander of the Royal Portuguese Military Order or Our Lady of the Immaculate Conception of
Viēosa Village, Judge, and chief of Police of the province of Piauhy
Hereby grant this passport to Captain John Robertson, naturalized Brazilian citizen,
"natural" of London, English Empire, son of
Guilherme Robertson, to go to England with stops at the ports within the itinerary.
Valid for four months from this date.