Prime Minister Lee Hsien Loong and Minister for Foreign Affairs Vivian Balakrishnan have written to Johor Sultan Ibrahim Sultan Iskandar to convey their condolences on the passing of Sultan Ibrahim's mother, Enche' Besar Hajah Khalsom Abdullah, last Friday, the Ministry of Foreign Affairs said in a statement.

The Johor palace's press office confirmed her death on Saturday morning. She was 83.

Sultan Ibrahim on Saturday also posted a tribute to his mother on his official Facebook page, accompanied by a black and white photograph of her.

Writing to Sultan Ibrahim yesterday, Mr Lee said he and his wife were deeply saddened to learn of her passing.

"Ho Ching and I are deeply saddened to learn of the passing of your beloved mother, Yang Amat Mulia Enche' Besar Hajah Khalsom Abdullah," he said, noting that Hajah Khalsom was well loved by the people of Johor.

"She was known for her warmth and generosity of spirit. I remember sitting beside her at dinner at the wedding ceremony of the Tunku Mahkota Johor. It was the first and only time we met, but we spent a pleasant evening having a good conversation," he said.

"She will be dearly missed. Our thoughts are with you and your family during this difficult period," Mr Lee added.

Dr Vivian also conveyed his condolences to the Sultan. "Her passing is a sad loss for the Johor Royal Family and all Johoreans. She will be dearly missed," he said.

The Johor Royal Court Council president Abdul Rahim Ramli said that Hajah Khalsom died at King Edward VII's Hospital in London at around 7.55pm (British time) last Friday.

He said her remains will be taken back to the state palace for the public to pay their last respects on a date and time to be announced later. The state flag is being flown at half-mast to mark her passing and will continue until the burial ceremony.

Hajah Khalsom, who was born Josephine Ruby Trevorrow, was married to Sultan Iskandar in 1956. She adopted the Muslim name Khalsom Abdullah after her marriage.