Catherine, Princess of Wales, in hospital after abdominal surgery

 Kensington Palace said the procedure was planned and successful but the princess is not expected to resume royal duties for months.

The palace did not disclose further details about her condition but said it is not cancer-related.

A statement added Catherine, 42, wished to apologise for postponing planned engagements.

"Based on the current medical advice, she is unlikely to return to public duties until after Easter," a statement said.

The Prince of Wales will not be carrying out any official duties while his wife is in hospital or immediately after she is discharged.

As is standard practice for senior royals, the palace has disclosed few details about the princess' condition and will not provide a running commentary on her recovery.

But it is clear from the length of time Catherine is expected to stay in hospital and the tone of the statement issued by the palace that her medical condition is serious.

The surgery - which took place on Tuesday - was significant enough to keep her in hospital for up to two weeks and it is expected that recuperation could take as long as three months.

Many minor conditions can be treated and the patient sent home shortly after.

The princess had a full diary in December and there was no indication that she was unwell during public appearances.

A statement from the palace said the princess "appreciates the interest this statement will generate" and stressed she wants her personal medical information to remain private.