An auction of George Michael memorabilia, including the guitar from his Faith video, has prompted objections from the family of his late personal assistant, whose estranged husband inherited the collection.

Sworders is offering 32 lots on Thursday from Siobhan Bailey’s collection. Her brother, Gerard Bailey, wants the sale stopped or advertised in Ian Belcher’s name rather than hers. He accepts Belcher’s legal right to sell, but argues that using his sister’s name misrepresents her wishes.

Siobhan died suddenly of natural causes in 2014, aged 56. She was divorcing Belcher but remained legally married to him and left no will, so her estate passed to him. Her brother says she had begun preparing a will leaving the possessions to her nieces and nephews, but it was not registered. That account does not alter Belcher’s ownership.

In a letter to Sworders, Gerard described the sale as a breach of his sister’s privacy and the use of her name as “disingenuous” and “wholly unethical”. He said she would have wanted the possessions kept within her family, who would never have sold them, and accused Belcher of deciding to cash in 12 years after her death.

Both Belcher and Sworders declined to comment on the objections. A separate explanation came from Sworders auctioneer Guy Schooling, who said Belcher had been traumatised by Siobhan’s death and kept the collection in his garage. He was later persuaded the items could not remain there indefinitely because they would deteriorate, Schooling said.

The most valuable lot is the vintage Gretsch Synchromatic acoustic guitar used in Michael’s 1987 Faith video, estimated at £60,000–£120,000. The video helped establish his solo identity after Wham!, the duo he formed with Andrew Ridgeley. Gerard says Michael gave Siobhan the instrument because he valued her so highly.

More personal possessions have also attracted bids. Her Filofax from the 1988 Faith tour, containing handwritten notes and annotations, had reached £1,750 against an estimate of up to £600. Other lots include a note from Michael and Ridgeley written “with love and admiration”, a signed Wham! photograph, an invitation to Ridgeley’s 21st birthday party and gold and platinum sales awards.

Siobhan began working for Michael in 1984, when Wham! achieved their first number one with Wake Me Up Before You Go-Go, and remained his assistant for 20 years. Michael died in 2016.

Her brother remembers her as a trusted, candid adviser who avoided publicity and protected Michael’s privacy. He says she would never have consented to selling such personal belongings. The dispute concerns those wishes and the presentation of the auction, not Belcher’s legal entitlement to proceed.