Cristiano Ronaldo has celebrated dozens of goals at Old Trafford but Tuesday's winner for Real Madrid against Manchester United was the first time he held up his hands in apology after scoring.
The Portuguese, who spent six years at United from 2003, completed a 2-1 comeback win for Real who went through to the Champions League quarter-finals 3-2 on aggregate.
He received a rousing welcome back before the match, but broke the home fans' hearts when he slid in at the far post after 69 minutes to sweep the ball into the net.
"It was an emotional moment for me. I just have one word to say - unbelievable. What the supporters do to me is they make me feel shy," Ronaldo, who also scored Real's equaliser in the first leg in Madrid, told Sky Sports.
As a mark of respect to the United fans who once adored him, he pointedly refused to celebrate his winner, shrugging his shoulders and lifting his arms as if to say sorry.
"It's respect for the affection that people gave me here over many years. Those are feelings that you don't forget," he added on Spanish television broadcaster TVE.
"I didn't celebrate but I was happy inside and what I wanted most was to win and step by step continue on our way to the final of the Champions League."
Before the match United manager Alex Ferguson remembered what the great Brazilian striker Ronaldo did for Real against his team a decade ago, when he scored a hat-trick at Old Trafford to help the Spaniards into the semi finals.
"Our main worry," said Ferguson on Monday, "was not what happened 10 years ago but what is going to happen tomorrow."
He was right to be worried.