Running through the fields with her newly-born foals, mare Royal Beatrice has good reason to celebrate – after managing the astonishingly rare feat of producing twins.

The 22-year-old New Forest Pony has shocked equine experts with the surprise birth of healthy twin foals because the chances of both surviving are so slim.

In nearly all cases, one or both foals die in a twin pregnancy because the mother’s uterus cannot support two babies.

The chances of a mare giving birth to healthy twin foals are about 1 in 10,000, experts said today.

But little filly Bess, and colt Royal, have defied the odds by becoming the first twins to be born in the New Forest, Hampshire for many years.

And at just a few weeks old, the playful pair are lapping up all the attention they are attracting from horse lovers across the country.

Royal Beatrice gave birth to the pair at St Leonards Farm near Beaulieu after mating with a spotted Appaloosa Cockaroost Pazaz stallion.

Bess and Royal can thank their father for their distinctive white markings and have been registered as First Cross New Forest/Appaloosa ponies.

Secretary of the New Forest Pony Breeding and Cattle Society, Jane Murray, said: “It is extremely unusual for horses to give birth to twins like this.

“To get both foals surviving to full pregnancy is a very rare feet indeed and we only have a couple of examples in our stud book of it ever happening before.

“But it is even more rare when the mare is so old. At 22, I think it’s fair to say that Royal Beatrice has done extremely well to have healthy twins.

“Her owners can be well and truly chuffed.”

Owner Stacey Gulliver from Beaulieu added: “Although my dad did mention she looked a bit fatter than is usual, it was a total surprise that it was twins, especially as they are so rare.”

The British Horse Society’s senior executive of welfare, Lee Hackett, said the overall chances of a mare giving birth to healthy twins are 1 in 10,000.

He said: “This is incredibly rare and it is wonderful news that both these foals have been born healthy.

“In most cases both of the foals will die during pregnancy, or if you are lucky one might manage to survive.

“Most owners will choose to abort as soon as they realise that the mother is expecting twins because they don’t want to risk losing the mare as well.

“Horses are just not designed to carry twins. The mother’s uterus is not large enough or well enough equipped to cope with them.”

He added that a mare’s placenta cannot support the needs of two growing foals once they reach a larger size in the later phases of pregnancy and therefore one or both die.

Twins account for around 15 per cent of all pregnancies in thoroughbred horses but in only 10 per cent of those cases will both foals survive to the point of birth.

And even if they make that far, only 15 per cent of those will result in a successful birth of two live foals.

The odds are even slimmer in cross-bred horses, Mr Hackett said.