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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Angela Kelly and her daughters, 12-year-old Shanti Harbourne, and Maya-Rose Kelly-Johnson, five, were last seen in Camberley, Surrey.
Voters in part of London have reportedly been turned away from polling booths due to "problems with the lists".
A fire on the tracks this morning at Vauxhall railway station is causing a headache for commuters with disruption until further notice.