Becky Watts' step-brother has been charged with her murder, police have said.
Nathan Matthews, 28, was charged on Wednesday, after Avon and Somerset Police announced it had discovered body parts in the search for the missing 16-year-old.
His girlfriend, Shauna Hoare, 21, has been charged with intending to pervert the course of justice.
The pair, both of Cotton Mill Lane, Bristol, will appear at Bristol Magistrates' Court on Thursday morning. They remain in police custody.
Four men and one woman arrested on suspicion of assisting an offender also remain in custody at this time, a police spokesman said.
Matthews and Hoare, who uses the surname Phillips on her social media accounts, were arrested on suspicion of Becky's kidnap on Saturday.
They were later rearrested on suspicion of her murder and detectives had until this afternoon to charge or release them.
A force spokesman said: "Nathan Matthews, 28, of Cotton Mill Lane, Bristol, has been charged with the murder of Rebecca Watts. He remains in custody and is due before Bristol Magistrates' Court tomorrow at 10am.
"Shauna Hoare, 21, of Cotton Mill Lane, Bristol, has been charged with intending to pervert the course of justice. She remains in custody and is due before Bristol Magistrates' Court tomorrow at 10am.
"The four men and one woman who were arrested on Monday on suspicion of assisting an offender remain in police custody at this time. A warrant of further detention was granted for these suspects at hearing earlier today."
Hoare was last night rushed to hospital by officers after "feeling unwell" in custody but returned after being seen by a doctor, police previously said.
Becky, described as "wonderful" by her family, vanished from her home in Crown Hill, Bristol at 11.15am on February 19.
Avon and Somerset Police launched a huge search operation - involving six police teams each day - after she was reported missing the following afternoon.
Bouquets, teddies and cards have been left at the family home where Becky went missing, and at the site where body parts were found.
The five people arrested on suspicion of assisting an offender following the grim discovery are four men, aged 29, 29, 23 and 23, and one woman, also aged 23.
Matthews was identified as the teenager's stepbrother - the son of her father Darren's wife Anjie - by family members.
Formal identification procedures of the body parts has not yet been completed.
Churches, such as St Luke's in Barton Hill and St Ambrose near to Becky's home, have opened for mourners to pay their respects.
Rachael Scott, head of the CPS South West Complex Casework Unit said she had been offering "advice and guidance" to police since the arrest of Matthews and Hoare.
"Having carried out a detailed review of the evidence gathered by Avon and Somerset Police, my conclusion is that there is sufficient evidence to charge Nathan Matthews with the murder of Becky Watts," she said.
"I have also concluded that there is sufficient evidence to charge Shauna Hoare with attempting to pervert the course of justice.
"Proceedings are now ongoing and the defendants have the right to a fair trial. It is very important that there should be no reporting, commentary or sharing of information online which could in any way prejudice these proceedings."