The Dutch striker left United under a cloud in 2006 after he fell out with the manager. The pair spoke on the phone earlier this year – Ruud told the press he "wanted to apologise... it was a shame it ended like it did" – but Friday's meeting, at a ceremony to unveil a Sir Alex Ferguson statue at Old Trafford, was the first time they'd come face to face since van Nistelrooy's exit.
"It's great to be back," Ruud said, "especially as it is to pay respect to the manager, who deserves all the credit for today. He's the reason we are here.
"I have a great five years and I want to pay my respects. I'm very grateful for the chances Sir Alex gave me.
"What stood out for me was Gary Neville's comment [in the ceremony's video tribute]. He's able to get the best out of people. He did that with me as well. Not just on the pitch but off it he gave me a lot, which I am very grateful for.
"Of course, we had our things with the way it ended at the club. But overall I look back on a great time here with a lot of respect for him."
Van Nistelrooy, who netted 150 goals for United in just 219 appearances, bears no grudge towards the man who called time on his Old Trafford career.
"When he is building new teams he is willing to do that [be ruthless]. That is all credit to him. The club is the most important thing.
"That is what he always said. It is his most-repeated sentence. He proves that. You move on. I moved