Scoring the winning goal to knock former club Manchester United out of the FA Cup filled Arsenal striker Danny Welbeck with mixed emotions.
Old Trafford academy graduate Welbeck was sold by United boss Louis van Gaal for £16m last September.
The 24-year-old's goal in the 2-1 quarter-final win earned Arsenal a first Old Trafford victory since 2006.
"Manchester United is a club that means so much to me," Welbeck said. "I'm a fan and it's hard to knock them out."
Welbeck, who joined United aged eight, was allowed to leave by Van Gaal because the Dutchman believed he did not score enough goals.
But his replacement in the Manchester United squad, Radamel Falcao, was left on the bench during the enthralling game at Old Trafford on Monday.
Welbeck, who celebrated the goal against his former club before later admitting he could not remember doing so, now has eight goals in all competitions this season compared to Falcao's four.
The England striker added: "I'll always respect the fans, I had a lovely reception from them and I'm thankful for that."
When asked if he stood by his decision to sell Welbeck, Van Gaal said: "Yes. A lot of times a player shall be very motivated against the club he played for, but I think we gave that goal [away]."
Arsenal boss Arsene Wenger praised Welbeck's impact during his first match back at Old Trafford with the win earning a semi-final tie against Bradford or Reading at Wembley.
"We all want to do well when we play against our former club to show we are great players," Wenger said.
"It is not easy to deal with the mental aspect of it. He focused just on his game and played football the way he wanted to. He has showed mental strength.
"He is intelligent. He is a great talent and has done extremely well for the national team as well."
Wenger also said his side's victory can boost their confidence for the rest of the season as they seek to repeat their 2014 FA Cup triumph, qualify for the Champions League and overturn a 3-1 deficit against Monaco in this year's competition.
"I believe the result can give us some good morale for the league and a very important Champions League game," the Frenchman said.
"Every win makes you confident. We have won at Manchester City and that helped us to win here," he added. "When you have won big games it is more mental. The belief is important."
Chief football writer Phil McNulty's analysis
Arsenal manager Arsene Wenger was under pressure and scrutiny after a display that mixed gross incompetence with naivety when they lost 3-1 at home to Monaco in the first leg of their last-16 Champions League tie.
And yet here at Old Trafford, scene of so many recent disappointments and a place where they had not won since 2006, the FA Cup holders confirmed a return to Wembley with an accomplished performance that mixed Wenger's traditional passing demands with a touch of steel.
As they had done when winning at league champions Manchester City earlier this season, Arsenal showed a mental block that had plagued them for seasons had been cleared.
Then, to add further pleasure, they drew either Reading or Bradford City in the semi-final. No easy tie - remember how Bradford unseated them on penalties in the 2012 League Cup quarter-final - but self-evidently the opponents the remaining sides would have wanted.
Arsenal are now overwhelming favourites to reach a second successive FA Cup final and the opportunity to retain the trophy won from two goals down against Hull City in May. Their season is likely to be alive until the last day with the possibility of another trophy.
And that, given Arsenal's faith in Wenger, is likely to be a shield against the critics who question (with justification it should be said) the lack of title challenges and struggles to reach the later stages of the Champions League.