Unfortunately, when they shifted the line west in the Atlantic, it also moved west on the other side of the globe.
Francisco Serrão was Portugal's man on the ground in the Spice Islands. Letters to his cousin, Fernão de Magalhães, seem to have suggested the islands might lie on the Spanish side of an all-important dividing line.
More significantly, since no one knew where the dividing line would fall, it might lie as far west as Malacca.
The cousins had sailed east on Francisco de Almeida 7th India Armada in 1505. While Magalhães had returned to Portugal after the Portuguese conquered Malacca, Serrão had survived two shipwrecks to wind up safe and sound among the cloves on the island of Ternate.
After further service in North Africa, where wounds left Magalhaes effectively lame, the Portuguese king turned down his request for a pension. So the injured party took his grievances to Spain.
After quite a deal of lobbying, Charles V gave the Portuguese renegade command of a five-ship expedition that would sail to the East Indies around the bottom of South America.
By this point, the Portuguese would almost certainly have encountered Australia's northern coast. They were already collecting sandalwood in Timor and would presumably have attempted to locate those fabulous territories beyond Java described in Marco Polo's Travels.
Under the circumstances, if they decided to do away with the man now known as Hernan de Magallanes (or, in English, Ferdinand Magellan), who would be surprised?
They had much to lose.
However, it would have to carried out discreetly, preferably in some out-of-the-way location.