The airline declared bankruptcy on Monday after failing to secure fresh capital or sell the business, leaving British authorities racing to rescue tens of thousands of customers stranded abroad, while Monarch staff were made redundant.
"Yesterday was a heart-breaking day as 2,000 people lost their jobs and we are all absolutely devastated for the customers and for all of us," Swaffield told BBC Radio 4.
The Civil Aviation Authority regulator launched an emergency repatriation scheme on Monday to fly back 110,000 Monarch customers to Britain at an estimated cost to taxpayers of 60 million.
Monarch has been badly hit by a legacy of weak demand in previously key markets Turkey, Tunisia and Egypt that have each suffered terrorist attacks in recent years.
In turn, the events have sparked fierce competition and oversupply for popular destinations Portugal and Spain.
Monarch therefore faced the daunting prospect of a huge loss for the next financial year.
"The figure was well over 100 million" (that the group was projected to lose next year) and we could not figure out a way of reducing those losses significantly," Swaffield said.