"I shall miss it. I was very happy here, but there comes a time, " nods the Princess of Stigliano Colonna.

For only the third time in 400 years, the Clonmannon Demesne Mansion House on 190 acres will be auctioned on 31 May at the Marriot Hotel, Druids Glen, Newcastle, Co Wicklow. Agents McDonnell Properties in Ashford have set an AMV of 5.6m.

The princess is moving to Monte Carlo. Her husband Prosper, a Roman prince and head of the house of Stigliano Colonna, has properties abroad and there is a lot of coming and going.

"Now that the children have all grown up I am sometimes lonely. I feel the time is right but of course I shall miss it here. It is very much a home.

We restored it ourselves and it has kept us very busy. There is still a bit to be done, certain things that we never got around to, and now that we are all 'over 30', " she says with a girlish laugh, "someone else will have to do them."

The princess bought the demesne in 1968 and lived in a Georgian house on the estate with her then husband and family. She had a permit to train horses and had a stud farm.

"I trained a few slow horses for trainer Vincent O'Brien.

'Slow' means they didn't win, " she explains with a smile. "It was a boarding stud as well, and Robert Sangster and a few others kept horses here."

In 1984, when she married her prince, they set about restoring the mansion that had been abandoned for over 150 years.

The Georgian home was later sold and some years later became the Clonmannon retirement village, subject of major controversy.

"I also sold the Gallops many years ago but kept a right of way to the sea. There is a lovely stony beach there."

Clonmannon Demesne is situated on the Sea Road from Greystones to Newcastle. The Old Mansion is approached up a long gravel driveway, secluded and private in the midst of its wonderful old trees and lawns, with lazy streams and ponds that uniquely feature an ancient stone and brick-built limekiln.

The property faces east overlooking its own lands to the sea.

"My husband Prosper loves Ireland too and for us it has been a great achievement to restore a ruin. We had to start from scratch. All we had was a book with some photographs of what it had been like. We stripped it right back, and as we worked, it was amazing how the rooms off the bedrooms were just right for bathrooms.

"People who have come to view the property have loved what we've done, " she said.

That makes her happy.

"I could see them falling in love with it. You'd have to, the atmosphere is fantastic. Over the years this house has given me a feeling of great love and security. I can't choose who'll buy it but I hope they will love it for the lifestyle."

She doesn't see the demesne being bought for development. "I wouldn't think so, we surround a lake."

It is a sportsman's paradise renowned for its wild duck and pheasant shooting. There are deer around and the welldrained wetlands are ideal for summer grazing.

"There is over 60 acres of top-class arable land. I am hoping that whoever buys it will love to hear the birds sing, and like the peace and quiet and calmness."

The Mansion is 443 square metres (4,769 square feet) and, with its striking frontispiece, is a monument to a bygone age which has no parallel elsewhere in Ireland.

Granted by King Charles to Sir Abraham Yarner, Master Muster General to Cromwell in 1666, the lands descended by marriage to the Truell family, who in 1956 sold the demesne to the late Sir Alfred Chester Beatty; on his death it was sold in 1968 to the present owner, then Frances Willoughby, and her family.

"When the restoration started there was just a front facade, no floors. The building had been neglected for over 150 years. There were two rooms at the back where the grooms slept.

"Basically you couldn't get into the house. It's amazing how much muck and soil had built up over the years. We took it out bucket by bucket and got a lovely surprise. We thought we had found a window but it was an entrance, " exclaims the princess.

They had unearthed the dungeon of the Tower House, in which a stone-arched cellar was discovered. It now serves as an impressive dining room.

The four-storey house also holds another secret. There is another, unopened area adjoining this space which should prove a delightful and rewarding challenge for the new owners.

From the moment you step through the impressive castlestyle front door with its original black cast-iron hinges and large antique key lock and latch system, the atmosphere is magical.

The pine architraves on the doorways of the inner hall are impressive and this area leads to the garden room. The staircase leads to a spacious landing.

Behind the staircase is a cloakroom and double glasspanelled door to a family room.

The well-appointed drawing room is on the right as you enter the hall. and is a bright, airy room with carpet, double pitch pine shuttered sash windows and window seats to enjoy views over the front gardens. The fireplace in splendid dappled-effect Cork marble with plum-toned slate hearth and basket inset.

You'll find the study through the arched pillared entrance.

This room enjoys windows with views both to the side and front lawns. The floor is carpeted and behind a curtain is the entrance to a secret side passage.

Follow the steps down the high-ceiling passage past the fitted bookshelves and wood panelled walls, brass and rope handrail and brick stairs to the dungeon dining room.

Originally the 'tower house', it has slate flooring and period window detail, stone walls with alcoves, Belfast sink, plumbing for a dishwasher, shelving and is adjacent to the second unopened room.

On this floor a passage leads to a cloakroom, office and laundry room fitted with wood and chrome units, sink and WC.

Princess Colonna loves the galley kitchen with its slate flooring, wood-panelled walls and built-in dresser.

"That table featured in the Golden Olive television commercial, " she says. "The table never grows old . . . do you remember it?" She leads the way through to the comfortable family room with slate flooring, exposed central ceiling beam, and raised brick fireplace with built-in wood burner stove and log storage underneath.

"I built that myself with a local man. The settee came from Lloyd Webbers. I bought it at an auction. It's very comfortable, all goose feather cushions. Kabul our Dalmatian has taken over and loves to sit on it."

Antique wood floors lead to the first-floor sitting room with its two windows overlooking the rear garden which is bathed in afternoon sun and is an ideal area for entertaining.

A special feature is the sunken Cromwellian Yard surrounded by a high stonewall on three sides with a galvanised roof on two facing walls. The western side of the yard has been converted from stables to a children's play area.

Off the small landing is a bathroom with a pretty etched-glass door, carpet, antique claw footbath, WC, bidet and basin. There is also a decorative washstand and power shower.

"Our friend Desmond Mackey used to find us wonderful architectural pieces. The bath was one of his finds. We had it re-enamelled and it is beautifully done."

Also on this floor is a bedroom, with carpet flooring, painted wooden ceiling, curtained wardrobe and access to a large attic space.

On to the second floor, where the landing has a fabulous array of arched square and round windows overlooking the front gardens.

Here there is another sitting room with carpet flooring, open red-brick fireplace with slate hearth and antique pine surround and mantle. Double sash windows with attractive wood shutters and window seats allow you to enjoy the garden views. There are two single bedrooms and another bathroom.

On the third floor is a spacious double bedroom with wood flooring, brick chimney breast with basket fire inset, painted and beamed vaulted ceiling with spotlights and a ladder to an extra sleeping den.

The small en-suite is an antique in itself with wood flooring, marble and wood wash stand with antique basin and brass taps, painted and panelled walls, separate shower unit with antique wood panelling and an antique flathead brass shower fitting.

The master bedroom is on the fourth floor with a brick chimney breast, vaulted and beamed ceilings with two large velux windows, attractive exposed brick walls and an ensuite bathroom, this time with a cast iron bath on raised antique wood plinth, mosaic mirrored tiles and dual aspect windows over the side gardens .

Outside there is huge potential to develop the land around house as wonderful water gardens (currently a natural water garden). On part of the lands adjoining Killoughter Lane, with gated access, there is a ruin of the old farm manager's house which may have development potential for a single dwelling (subject to planning permission).

Price: AMV 5.6m at auction 26 May Agent: McDonnell Properties, Ashford, Co Wicklow (0404-28428)