They race together on spindly legs, lie side-by-side on the warm grass and play happily in a tangle of hooves.
With such a bond, it's no wonder that Leo and Corby were able to share their mother's womb successfully.
Healthy twins like them are a rarity among horses, as one embryo tends to take over during pregnancy and the other is aborted, or dies early.
The chances of Leo and Corby surviving were just one in 10,000, experts say.
Their owner Becky Passmore, an equestrian groom from Taunton in Somerset, said their birth three weeks ago came as a complete surprise.
She said their mother Georgie Girl looked larger than expected but there was no indication she was carrying twins.
'When I went to the stables around 2am, I could see Georgie Girl through the window and she was standing quite happily. I was pretty shocked when I opened the door and a foal fell out,' said Miss Passmore.I picked it up and put it in a straw bed and went to leave, but then I saw another foal curled up behind the water buckets. I couldn't believe my eyes.'
Miss Passmore, 21, said the babies had to be put in intensive care at the vet's for two days as they were two weeks premature.
When they came home, she bottle-fed them and slept in the stables. 'Gradually I let them be because they get stronger and stronger every day, though they're still very wobbly on their legs,' she said.
They are nearly identical, but Leo has a slightly bigger star on his forehead.
Nicola Jarvis, senior veterinary surgeon at horse sanctuary Redwings, said it was incredibly rare for twin foals to survive. 'Although mares quite often conceive twins, it is rare that both embryos survive,' she said. 'If you have two foals, they are vying for space and the chances of them coming out alive and well are slim.'