Nicky Hilton Rothschild is reportedly pregnant.

The 33-year-old heiress is said to be past her second trimester with her and husband James Rothschild's second baby and couldn't be happier to be adding to their family.

Nicky - whose daughter Lily-Grace turns one on Saturday (08.07.17) - was said to have confided in friends at Princess Olympia and Prince Pavlos' joint birthday party over the weekend.

A source told ''It was a Marie Antoinette costume themed party so she was wearing a corset so no one could tell.

''It's Lily's first birthday July 8 so they are excited. They always wanted to give Lily-Grace a sibling close in age, like they both have.''

Nicky is due to give birth in early 2018 and the source admitted she and James would ''love'' to have a boy, but would equally be pleased to have another girl.

The socialite's mother, Kathy Hilton, previously praised her daughter's parenting skills.

Speaking just a few months after Lily-Grace was born, she said: ''She's unbelievable. Her computer and her phone have just been in the same place. We spent a month together out in the Hamptons and she's breastfeeding and it's a full time job - literally a full time job - so she can't go anywhere for more than an hour. I think we went out twice.''

And Nicky has a much more scheduled approach to motherhood than her own mother did.

Kathy added: ''With my babies, if I wanted to go pick them up I would just go in the room in the middle of the night, but Nicky is very much on a schedule. This is nap time, this is tummy time, so I'm just kind of like, 'Okay' ...

''I'll tell her certain things, but she's read up on everything.''