LONDON (REUTERS) - Britain's Prince William, second-in-line to the throne, launched a new career as an air ambulance helicopter pilot on Monday, saying his new job would keep him "a good guy".

William, Queen Elizabeth's grandson who was previously a search and rescue pilot with the Royal Air Force, will fly missions from Cambridge Airport with specialist doctors and paramedics across eastern England.

The prince, 33, who became a father for the second time in May with the birth of daughter Charlotte, said he was"fantastically excited" about the role.

"Doing a job like this is worthwhile, valuable and to me there is an element of duty about it," he said in a televised interview for media.

"For me, it's also a really important point to be grounded and I feel doing a job like this really helps with grounding the core of what I'm trying to become."

Asked what that was, he replied: "Trying to be a good guy, trying to do what you can and trying to be a decent individual."

Whilst the air ambulance role will be William's primary job, he will continue to carry out official duties as a royal, responsibilities which have grown in recent years as the 89-year-old queen scales down her engagements.

"The queen is still very active and is still showing incredible leadership," said William, who is known as the Duke of Cambridge. "My father (Prince Charles) is doing many, many engagements, as are the rest of the family. I hope to still be a part of that ... but equally do something that I think is incredibly important and that will prove me in good stead for the future."

The new job means he, wife Kate and his children, Prince George, who celebrates his second birthday later this month, and baby Charlotte, can live at Anmer Hall, their country mansion on the queen's Sandringham estate in Norfolk, eastern England.

"At some point there is going to be a lot more pressure and responsibility from the other side of my life, but at the moment I'm juggling the two of them and a young family and I'm enjoying it and I like the challenge," he said. "Inevitably down the line things will probably become a little more difficult for me to do that."

He described Charlotte as a "little joy of heaven" and said looking after two little children took more responsibility. "Especially when George is around - he's a little monkey,"William said.