"It's a reality check," Hartley told British media. "We have got to take the positives from it and how I see that is that we are not the finished article.
"There will be lessons to be learnt from this game. It will keep us focussed and working hard to improve."
England won the tournament last week after thrashing Scotland and collected the Six Nations trophy in Dublin after Saturday's match, but Hartley admitted their triumph was tarnished by the loss.
"We don't have a game next week to rectify and put things straight. It's a bad taste. But we set out to win the championship and we've done that," the New Zealand-born hooker added.
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(Reporting by Shravanth Vijayakumar in Bengaluru; Editing by Toby Davis)
