Pique came through Barça's youth system but moved to United, aged 17, before struggling with homesickness during four difficult years at Old Trafford.
Now a World Cup champion and four-time Champions League winner, Pique has explained how at United his phone once went off in the changing room, prompting Keane to let loose.
“It's dead quiet. All of a sudden, you could hear this little vibration. Very soft,” Pique told the Players' Tribune.
“I realise it's me. It's my cell phone. I left it on vibrate, and it's in the pocket of my pants, stuffed in the clothes bag that's hanging right behind Roy's head.”
Pique continued: “He screams out to everybody, 'Whose phone is that?!' Silence. He asks again. Silence. He asks a third time. 'Whose. Bloody. Fucking. Phone. Is. That?!' Finally, I spoke up, like a little boy. Very softly, I said, 'I'm so sorry. It's mine.'”
Pique added: “Roy lost his mind! He went nuts in front of everybody! It was incredible. I almost shit myself. But it was a good lesson.”
With Nemanja Vidic and Rio Ferdinand ahead of him, Pique never managed to hold down a place at United and, in 2008, Ferguson sanctioned his return to Barcelona.
“I was honest with him (Ferguson),” Pique said. “I said, 'Listen, I feel like I've lost your trust. Barcelona is my home. I want to go back. I hope you will let me go.'”
Pique thought he would face his boyhood team when United then drew Barça in the Champions League but, before the semi-final, Ferguson paid a visit to the defender's hotel room.
“I knew something was going on, because he never came to see players before the match,” Pique said.
“I opened the door and he said, 'Gerard, I regret to inform you that I can't play you today. The deal is almost done. If I play you, and you have a bad game, they'll say it's because you're headed to Barcelona. So I can't put you in. I just want you to know why.'
“The truth is, I was pretty devastated. Even though I wanted to go home, I was ready to give everything for United and Sir Alex in that match. It was my dream to play at the Camp Nou in the Champions League.
“It hurt very badly. But in the end, Sir Alex made the right decision.”