Complex sentence: Green (1850), p.343 Ralph de Monthermer, 1st Baron Monthermer, and Joan of Acre blind-sided her father with this secret while he was already planning another marriage for his daughter to Amadeus V, Count of Savoy.
Split into simpler sentences: Green (1850), p.343 Ralph de Monthermer, 1st Baron Monthermer. Joan's father was already planning another marriage for his daughter to Amadeus V, Count of Savoy.