Oman's Sultan Qaboos returns from medical trip to Germany
Sultan Qaboos, who has suffered from an undisclosed illness for several years, visited the EU state for a medical check-up, described as a "total success" by state television.
The 75-year-old spent around two months in Germany and returned "after completing routine medical examinations... which showed good, hoped-for results," said the statement.
A similar visit was made in 2014, with Sultan Qaboos returning eight months later in March 2015.
The monarch has made little public appearances since returning from the last trip with speculations emerging on his condition.
Although no official statement has been issued on the nature of his illness, a diplomatic source in Muscat suggests the monarch suffers from colon cancer.
Qaboos is the Arab world's longest serving ruler and has overseen a massive development programme for the country since he took charge in 1970, using the country's oil wealth to bring it up to speed with its Gulf neighbours and transforming the fortunes of its population.
The leader has maintained neutrality amid escalating tensions in the region and has often been the go-to mediator between warring factions.
Questions remain over who will inherit the throne when the unmarried leader dies, as he has no heirs and has not yet designated a successor.