It happened when they were on their honeymoon. "It," of course, being The Great Shift. Ted was nearly devastated when he was separated from Joan almost immediately after they had checked into their hotel. It took three days for them to finally find each other. Ted was determined to be all the man that he could and carried Joan around for a bit once they found each other again. This was despite the fact that Ted was in a body significantly weaker than the one he had, and despite the fact that Joan was now in a body just a little bit heavier than the one she had.