Sir Clive Woodward says the bubble has finally burst for England as their bid for a record 19th consecutive win as well as back-to-back Grand Slams was quashed by Ireland in a 13-9 loss in Dublin on Saturday.
The four-point defeat was the first under Eddie Jones since the Australian took on the role as England head coach following a dismal 2015 World Cup campaign.
And Woodward -- who coached England to World Cup glory in 2003 -- felt the loss had been brewing since the start of the Six Nations in February.
"That was much more than a reality check," Woodward wrote in his column for the Daily Mail.
"The mystique which takes time to build was smashed in Dublin and Ireland won with something to spare. The bubble has finally burst.
"The world record-equalling run is over and that is probably no bad thing because there is much work to do, as most people appreciated. Certainly Eddie has never stopped stressing that.
"England were well beaten and bear in mind that they could easily have lost to France and Wales, too. They did very well to quarry out two wins there but the truth is that the champions might easily have finished third or fourth."
Woodward believes Jones must make some difficult decisions as he enters 'Phase Two' of his tenure.
The former England coach questioned the future of captain Dylan Hartley, James Haskell and Mike Brown as Jones builds towards the 2019 World Cup.
"Now sees the start of Phase Two, starting with the summer tour to Argentina with a squad that will be shorn of Lions," Woodward said.
"Selection must be more ruthless than ever.
"If they are going to be too old, not quite good enough or cannot be trusted to have the fitness to go head to head with the All Blacks for 80 minutes, then a parting of the ways must come now -- if World Cup success is to be achieved."