Pokémon : S5 | E44 – Great Bowls of Fire!

Moments after Team Rocket escaped in the arms of a Dragonite, Ash and his friends see Ash's Charizard approaching them from the sky. As Charizard lands on Ash and licks his face, Ash says that he hasn't changed a bit. Charizard is quickly followed by Liza, astride Charla's back, with whom both Ash and Clair are acquainted. It is revealed that Liza and Clair were good childhood friends and that Liza occasionally brings the Charizard from Charicific Valley to the Dragon Holy Land to train. Clair admits that she had seen Ash's Charizard before, but wasn't aware of his original Trainer. It seems that Charizard also has a romantic relationship with Charla, causing Brock to lament that he seems to be the only one here without any luck in love.

Liza asks Ash if he's had his Gym Battle with Clair, prompting the group to brief her on their recent troubles: Team Rocket stole the Dragon Fang, escaped into the Dragon's Holy Land, and tricked its guardian, Dragonite, into assisting them. Liza, Charla, and Charizard immediately pledge their assistance, and the group is soon towed across the Holy Land in Charizard-pulled balloons. As they fly, the group wonders why Dragonite would assist Team Rocket. Brock suggests that the criminals threatened to destroy the Dragon Fang, thereby forcing Dragonite to obey them, but Clair doubts that a Pokémon as intelligent and powerful as the Holy Land's Dragonite would fall for such a ruse. Kaburagi reminds Ash and his friends that Dragonite originally belonged to the first Blackthorn Gym Leader, who had dedicated his life to protecting the Holy Land; even after he passed away, his Dragonite continued her vigil in memory of her Trainer.
(Source: Bulbapedia)