there's some insinuation that Hal's biological father could be the medical attache:
-- Hal's "atavistically dark-complected”
-- they share an interest in byzantine erotica
-- from what i remember, dates and ages line up correctly to put Avril and attache both attending Brandeis a yearish before Hal is born
-- there's a reference or two to James finding that specific affair particularly upsetting
-- Avril's said to have a preference for sleeping with Canadians
-- the attache is "one-half ethnic Arab and a Canadian by birth and residence"
so Hal could potentially be 1/4 "near-eastern"