In 1969, Christian was purchased, when he was a very young cub, from a zoo by the London's Harrods department store and kept locked up in a cage in the basement. One night, Christian escaped from his cage and destroyed some of the merchandise at the store. The store manager became eager to get rid of the troublesome cub and decided to sell it immediately when was asked by John Rendall and Anthony "Ace" Bourke who, upon seeing him locked in the store's basement, fell in love with the little cub and decided to care for him.
Rendall and Bourke cared for Christian in their London apartment till he became a year old then, due to Christian's growing size, decided to move him to the basement of their own furniture store where they created living quarters for the young lion. They even obtained permission from a local vicar to allow Christian some exercise time at a church graveyard and took him regularly on car rides and day trips to the seaside.
As Christian became bigger and bigger, Rendall and Bourke found it more difficult to keep him in London and decided to reintegrate Christian into his homeland: the African wilderness of Kenya. They were assisted by George Adamson who was a British wildlife conservationist, commonly referred to as the Father of Lions as he was able to raise and introduce lions to the wild successfully.
In 1971, after hearing of Christian's successful introduction into the wild, Rendall and Bourke decided to visit Christian but were told by Adamson that Christian might not remember or even recognize them. Rendall and Bourke decide to try nonetheless and were filmed in a documentary titled Christian, The Lion at World's End.
The below clip from Christian The Lion shows the touching moment of reunion between the fully grown Christian and his old friends who rescued him from a metal cage when he was a tiny cub, raised and cared for him for so many months.
here is a more detailed article about Christian by the Daily Mail titled Christian, The Lion who Lived in My London Living Room.