London Zoo has welcomed its first ever baby sloth, after a surprise pregnancy.

Zookeepers were dealt a huge surprise in the Rainforest Life exhibit at ZSL London Zoo when female sloth Marilyn was found to be pregnant – as they didn't even know the male and female had mated.

Male Leander arrived from Germany at the end of 2012 to be paired with ZSL London Zoo's resident female Marilyn, but despite their ploys to get the pair together, keepers had no idea that the sloths had even acknowledged one another, let alone successfully mated.

However, it would appear that after hours, when away from the watchful eye of zoo staff the pair had, quite obviously, hit it off.

Two-toed sloths have been known to take almost a decade to form a pair bond and mate, but factoring in Marilyn's estimated 11-month gestation period, it took the Zoo's frisky pair just six months.

Video Courtesy of ZSL London Zoo