The US hunter who killed Cecil the lion, has issued an apology stating that he "deeply regrets" his actions and did not realise the majestic animal was so revered.

The 13-year-old prized lion was lured from Hwange National Park, a Zimbabwean nature reserve, on 1 July. He was shot with a crossbow, before being tracked for 40 hours and then shot with a rifle. The lion was then decapitated and skinned for trophies.

Conservation groups expressed shock after the lion was shot dead. Cecil was a popular attraction to the park and wore a GPS tracking collar as part of a University of Oxford research project.

Walter Palmer, 55, from Minnesota, was exposed as the lion hunter, as it was revealed he paid £35,000 ($50,000) to shoot the much-loved animal with a bow and arrow, reports the Telegraph.

Palmer told his local newspaper, The Star Tribune, he believed his hunting trip was completely legal.

In a statement he said: "I hired several professional guides, and they secured all proper permits. To my knowledge, everything about this trip was legal and properly handled and conducted.

"I had no idea that the lion I took was a known, local favourite, was collared and part of a study until the end of the hunt. I relied on the expertise of my local professional guides to ensure a legal hunt.

"Again, I deeply regret that my pursuit of an activity I love and practice responsibly and legally resulted in the taking of this lion."

Johnny Rodrigues, head of the Zimbabwe Conservation Task Force Conservation told Sky News: "The professional hunters scented the area by dragging a dead animal ... and lured the lion to this spot. And then they came in at night while the lion was feeding, with a spotlight, and shot it with a bow and arrow.

"They didn't kill him straight away. They took 40 hours to do a follow-up and eventually they caught up with him and shot him with a rifle."

The Zimbabwe Professional Hunters and Guides Association (ZPHGA) confirmed in a Facebook post that one of its members, Theo Bronkhorst, was also involved in the hunt.

A professional hunter, Bronkhorst contacted authorities the day after the lion was killed to say a mistake had been made. He and Honest Trymore Ndlovu, the owner of the land bordering the park, have been arrested and charged with illegally killing the animal.

The ZPHGA has confirmed that Bronkhorst's membership has since been suspended indefinitely.

A statement said: "ZPHGA re-iterates it will not tolerate any illegal hunting or any unethical practices by any of its members and their staff".

The Zimbabwe Parks and Wildlife Management Authority, who are responsible for issuing hunting permits and quotas, insist Cecil was killed illegally.

They said: "The killing of the lion was illegal since the land owner was not allocated a lion on his hunting quota for 2015. Therefore, all persons implicated in this case are due to appear in court facing poaching charges."

Both men are due to appear in court on Wednesday 29 July on poaching charges. If convicted they could face up to 15 years in prison.

Mr Rodrigues added that now that Cecil is dead, the next lion in the hierarchy, Jericho, will most likely kill all Cecil's cubs so that he can insert his own bloodline into the females.

The Star Tribune reported that Mr Palmer's dental surgery was closed on Tuesday, with a note directing reporters to a public relations firm.