I always called my mum “Sandy”. Once, as a kid, I asked, “Can I call you Mum?” And she said, “Of course, and I’ll call you Sonnypie.” From the age of six, after she split from my stepdad, it was just the two of us. There were lots of rude words and giggling, listening to music and dancing, and she was proud of me when I became a musician. When my wife and I had our first daughter, she became Grandy, but she never met our youngest.

In May 2016, she started getting bad headaches, and the next month, we had a diagnosis: a brain tumour. She had three months to live, at 66. It was crushing, but seeing Sandy ask her sister Norah to look after me was also beautiful. That night, she texted me about a drive we’d been on together in ridiculous rain, when she’d parked up and we’d lain in the road and the rain just hit our faces. I cried and cried.

Sandy didn’t want hospitals, pain and palliative care – she just wanted to die. It was so intrinsic to who she was that, in a funny way, none of us was surprised by her decision. But while you spend your whole life worrying about dying, when it comes to wanting to do it you realise how difficult it is. She found a load of morphine from when her sister was dying of cancer, and decided to take it. But the attempt failed, and that’s when she decided to go to Dignitas.

We spoke to someone who had travelled to Dignitas with their loved one and was happy to speak to us about their experience. Sandy emailed Dignitas, letting them know she had a deadline of less than three months. Then she started the process of collecting letters and documents, and transferring money – it would cost £12,000 all in.

The next weeks were precious. I’d spend half the week with Sandy at her home in Oxford, the other half with my family in London while Norah took over, and every weekend we would all have a big Sunday lunch together. She didn’t have any other visitors: she didn’t want to be at her funeral before she died. We danced in the front room, drove to the country listening to playlists of her favourite music, watched films like Die Hard and one awful Adam Sandler movie. She sat in her bed in an opiate high with the sun beaming down and a breeze through the window.

She got the green light from Dignitas and Sandy, Norah and I flew out in August. The doctor came to our hotel and asked her, over and over, “Is this what you want?” She bit his hand off.

The next morning, I remember Sandy, Norah and I laughing at the word ausfahrt in the cab, before the building came into view. Volunteers welcomed us, then there were more interviews and more documents to sign. Sandy took the first vial of liquid to line her stomach, then we walked around the garden to wait the half hour before she could take the next step. We had tea and a biscuit, and Sandy sat on the sofa between Norah and me and we hugged, before she took the final vial.

When she turned to me, I did an over-the-top wave and said a cheery “Goodbyeeee!” and she giggled. Then she went to sleep in our arms and died about an hour later. It’s only supposed to take 10 minutes – that’s how strong her body still was. Driving back from the airport next to an empty seat, I thought, thank God she got there in time.

Throughout it all, I was writing music: I recorded a song on my phone in the car park after the diagnosis; on all the drives to Oxford; and lying next to her when she was asleep. It was very therapeutic, but also sad because she wanted to listen to the songs: I couldn’t play them to her without leaving her for a few weeks to record them. Now it’s an album she’ll never hear. What shocks me most is that the thing I was so scared of throughout my childhood ended up being a moment of such freedom; that the experience of Sandy’s death brought so much good into our lives.

• As told to Moya Sarner.

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