STOCKHOLM (AP) — Sweden's King Carl XVI Gustaf will undergo a planned a keyhole surgical procedure "in the heart area,” the palace said Tuesday.

The official announcement did not elaborate on the nature of the surgery. The king is not known to have had surgery for a any serious ailment before.

After the surgery, scheduled for Feb. 20, the 76-year-monarch will take a rest period, meaning that his planned commitments this month and in early March will be pushed back to later this spring, the royal household said.

“The king is doing well and his official program until the day of the operation is being carried out according to plan,” the palace added in statement.

The king ascended the throne on Sept. 15, 1973 and is the longest reigning monarch in Sweden. Later this year, the king will celebrate his 50 years on the throne.

The royal family is hugely popular in Sweden. The monarchy enjoys widespread support despite the egalitarianism that otherwise characterizes society in the Nordic country.