It has never actually happened, yet. Chronologically, the earliest we've seen of the pair is in a flashback to when Luffy first got his devil fruit powers. The two had already known each other for some time at this point. Then throughout the rest of the eps, all the way up to today, Luffy hasn't met him again. The closest was when both were at Marineford, though Luffy was unconscious and Shanks declined to see him, saying it would forcibly break Luffy's promise to him.
for now... ep 316
It is in Episode 461, 'The Beginning of the Battle! Ace and Whitebeard's Past". Ace meets Shanks in a cave, thanking him for saving his brother Luffy.
The previous members of the Yonkou were - 'Red Haired' Shanks, Whitebeard, Kaidou, and Charlotte Linlin, aka 'Big Mam'. Whitebeard has since been killed, but after the timeskip, Blackbeard is now considered the fourth Yonkou after Whitebeard's death.
Whitebeard
Whitebeard's bounty was never revealed.
They haven't explained 'how' just yet. The only thing we know is the Yami-Yami no Mi is partly gravity-based, so 'pulling' the power from Whitebeard is one possible answer.
Episode 316.
It is in Episode 461, 'The Beginning of the Battle! Ace and Whitebeard's Past". Ace meets Shanks in a cave, thanking him for saving his brother Luffy.
episode 316
The previous members of the Yonkou were - 'Red Haired' Shanks, Whitebeard, Kaidou, and Charlotte Linlin, aka 'Big Mam'. Whitebeard has since been killed, but after the timeskip, Blackbeard is now considered the fourth Yonkou after Whitebeard's death.
Whitebeard
Whitebeard's bounty was never revealed.
Ace was the 2nd Division Commander in Whitebeard's crew.
Bob Shanks's birth name is Robert Horton Shanks.
Wes Shanks's birth name is Wesley J. Shanks.
Whitebeard in One Piece is 72 years old at the time of his death in the series.
Shanks Pony Is An Expression Which Means Walk
Shanks Group's population is 4,246.