Summary: The Doctor wants to do something special for Donna.
Of all his companions, Donna was the one the Doctor felt worst about leaving behind. All the others had at least been able to look back on their adventures and benefit from everything they’d learned, but Donna had blossomed so much only to have it all snatched away to save her life.
Now, knowing he would soon regenerate, the Doctor wanted to see her again.
He’d already visited his other recent companions, checking on them and lending a hand, but for Donna he wanted to do more than throw confetti at her wedding.