Considering the fact that A Song of Ice and Fire is described by the author as somewhat inspired by the Wars of the Roses, one only needs to look at the final decisive battle in that series of wars, the Battle of Bosworth.

The Frey equivalent in this case would be Lord Stanley who betrayed Richard III at the battle. He was of dubious loyalty to Richard III, although he hadn't been found guilty in the attempted coup against the king in 1483, and was the step-father of Henry VII. Richard III had detained Lord Strange, the son of Lord Stanley to ensure his loyalty.

Richard III intercepted the army of Henry VII with the forces of Lord Stanley nearby. When Henry VII made the first move to attack, Richard III allegedly called upon Stanley to engage Henry VII or the life of his son would be forfeit and was met with an indifferent reply stating, "Sire, I have other sons".

Lord Stanley didn't immediately join in the battle, instead he waited until he saw Richard III in a vulnerable moment and rode into battle to support Henry VII. When Richard III was killed Stanley allegedly crowned Henry VII with Richard's crown.

Um... yes. Yes it has. From the Wiki of Ice and Fire:

"George R.R. Martin has revealed that the inspiration for the Red Wedding came from the Black Dinner. The Black Dinner took place in 1440 when William Douglas, the 6th Earl of Douglas, was invited to a dinner with the ten year old King James II of Scotland. After the dinner the Clan Douglas chiefs were taken outside, given a mock trial and beheaded."