Complex sentence: The Heungseon Daewongun seemed open to this idea, but it was possibly a ruse to bring the head of the Korean Catholic Church out into the open; upon Berneux's arrival to the capital in February 1866, he was seized and executed.
Split into simpler sentences: The Heungseon Daewongun seemed open to this idea, but it might have been a ruse to bring the head of the Korean Catholic Church out into the open. Berneux was summoned to the capital, but upon his arrival in February 1866, he was seized and executed.