Criminal offence

Robert was suffering from stress after being made redundant and losing his mother. He was also facing eviction within days, and sought comfort in half a bottle of vodka before leaving his flat one night. He was walking through the park when he thought he saw his girlfriend – Jenny – with another man. Robert lost his temper and ran up to them both. The mystery man ran away. Robert collided into Jenny and punched her relentlessly until there were no signs of life. Robert ran away crying, now counting “his girlfriend” on his list of things that he had lost forever. It later transpires that the girl was not Jenny, but Robert is still arrested by police and taken in for questioning after a witness recognised him. He alcohol level is found to be over the legal driving limit.
This is the question

Robert has asked you, as his criminal lawyer, whether he can be charged with an offence and whether he has a good excuse. Identify a relevant criminal offence that he may be charged with and any relevant defences that he might use, and apply them to the facts of his case to advise him.