London Zoo says it believes Melati carried the cub outside, but keepers are unclear as to how the cub got into the pool.
Keepers are now reviewing the situation because it was not forseen that the mother would take the cub outside so early.
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An English springer spaniel given to the UK Border Force has become a star new recruit for sniffing out smuggled cash.
Celine Dookhran, 20, was allegedly kidnapped by her relative Mujahid Arshid, 33, and his employee Vincent Tappu, 28, on July 19 last year.
Collins hid the device, two sim cards and two memory sticks inside a crutch while on remand in September.