I didn't think Robert George Fortt jr had any children I hope he did but it doesn't look like it.
only his brother Edward appeared to have a Child and moved to Canada.
Ronald Larner Fortt
B:28 May 1888 Victoria, Ontario, Canada
D:23 July 1956 Victoria, Capital Regional District, British Columbia, Canada
Ronald had a son "Edward William Ronald Fortt" who married a Cynthia Hope but was killed in WWII at the age of 22 with no Children.
Ronald's Daughter
Beatrice Joan Fortt also in Canada married later in life but had no children.
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both Robert jr sisters' had no Children
Harriet Laura Fortt died in 1940 under the same name
BIRTH 23 FEB 1860 • Cheltenham, Gloucestershire, England
DEATH 28 MAY 1940 • Cheltenham, Gloucestershire, England
so likely never married the 1939 Reg says she is single.
so unless anyone can fin other wise I assume never married and had no Children.
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Robert's other sister Florence Mary Fortt
died in 1929 the obituary mentions her under the same name and says nothing of a marriage or children
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so that is it for Robert Fort Snrs line