Indian forces have been fighting the rebels for two decades

Prince Jigyel Ugyen Wangchuck, known as Jigs to his friends, flew home on Tuesday morning, just four weeks after starting as a fresher at St Peter's College.

The 19-year-old, whose father is the "Dragon King" of Bhutan, is leaving behind a politics degree to join a battle to expel separatists using the Buddhist kingdom to launch attacks against India.

The separatists are fighting to break Indian control of the state of Assam, and have been operating training camps in southern Bhutan's forests.

I love Oxford because I can be Jigyel, not constantly in the spotlight like in Bhutan Prince Jigyel Ugyen Wangchuck

"Regardless of who I am, I've taken an oath of allegiance" the prince told the Oxford Student newspaper before his departure from Heathrow Airport.

"Although I was happy here in this amazing city, I've done the right thing."

He said he joined Bhutan's militia without his parents knowledge after leaving high school in the United States last summer.

He underwent two months of intensive training.

The prince said his mother was "disappointed" that he was giving up the chance to study at Oxford, but he had "no regrets".

He said he had enjoyed his short time in the city.

"I love Oxford because I can be Jigyel, not constantly in the spotlight like in Bhutan," he said.

The prince's father, King Jigme Singye Wangchuck, 48, a soccer fanatic educated in India and Britain, is the fourth king of Bhutan, which lies between India, Nepal and China.

He came to power in 1972 as an absolute ruler but has moved to create a parliamentary democracy.

He had called for talks between his government and the rebels, but they broke down this week.