Former Love Island contestant Montana Brown has said that Mike Thalassitis was in a "dark place" in the months before his death.
Brown appeared in the 2017 series of the ITV2 show alongside Thalassitis, who has died aged 26.
LONDON, ENGLAND - FEBRUARY 07: Mike Thalassitis arrives at BUILD Series LDN at AOL to talk about Celebs Go Dating on February 7, 2018 in London, England. (Photo by Neil Mockford/GC Images)
Mike Thalassitis at a BUILD - Celebs Go Dating special at Shropshire House, London.
File photo dated 16/10/2018 of former Love Island contestant Mike Thalassitis who has died aged 26, his management has confirmed.
File photo dated 7/2/2018 of former Love Island contestant Mike Thalassitis who has died aged 26, his management has confirmed.
Mike Thalassitis attending the UK premiere of Daddy's Home 2 held at Vue West End, London
Chyna Ellis (right) and Danielle Sellers with Mike Thalassitis attending the UK premiere of Daddy's Home 2 held at Vue West End, London
Mike Thalassitis and Danielle Selllers attending the ITV Gala 2017 held at the London Paladium, London. Photo credit should read: Doug Peters/EMPICS Entertainment
Mike Thalassitis and Danielle Sellers attending the ITV Gala held at the London Palladium. Picture date: Thursday November 9, 2017. See PA story SHOWBIZ ITV. Photo credit should read: Ian West/PA Wire.
LONDON, ENGLAND - JANUARY 10: Mike Thalassitis and Montana Brown seen on a night out at Sexy Fish on January 10, 2019 in London, England. (Photo by Ricky Vigil/GC Images)
LONDON, ENGLAND - JANUARY 10: Mike Thalassitis seen on a night out at Sexy Fish on January 10, 2019 in London, England. (Photo by Ricky Vigil/GC Images)
LONDON, ENGLAND - JULY 21: (L-R) Mike Thalassitis and Megan McKenna attend Kisstory On The Common 2018 at Streatham Common on July 21, 2018 in London, England. (Photo by Jeff Spicer/Getty Images)
LONDON, ENGLAND - JUNE 29: Megan McKenna and Mike Thalassitis sighting in Soho on June 29, 2018 in London, England. (Photo by GORC/GC Images)
LONDON, ENGLAND - NOVEMBER 09: Mike Thalassitis attending the ITV Gala afterparty at Aqua on November 9, 2017 in London, England. (Photo by Mark R. Milan/GC Images)
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In a tribute on Instagram, she said she wished she had done more and revealed he had turned to self-help books in recent months.
Reality television star Thalassitis died on Friday, his management confirmed, with reports suggesting he was found near his home in Essex.
Brown also revealed details of their last phone call, in which Thalassitis congratulated her on a recent swimwear launch.
She said: "Now I know you were in a dark place a few months back and I thought you were past it and that you were on the up.
"I got you to buy (self-help book) The Magic, you wrote down your gratitudes, you had the pictures of your family in your car to remind you to be grateful for them.
"I just don't know how I didn't notice... I am absolutely heartbroken that I couldn't help you.
"Your phone call a few days ago to tell me that I'm smashing the swimwear, you're proud of me and that you're grateful for my friendship is the only thing that's keeping me going right now.
"At least you knew how much you meant to me."
Thalassitis found fame on the 2017 series of the ITV competitive dating show, earning the nickname "Muggy Mike" after partnering with fellow islander Chris Hughes' girlfriend Olivia Attwood.
Brown added: "I've thought long and hard about what I want to say, I've woken up and unfortunately this wasn't just a nightmare so this is to you Mr Thala.
"Firstly, I'm so angry at you for doing this because you are so loved by so many people and I just wish you picked up the phone so we could've sorted this out. This didn't need to happen.
"Secondly, it annoys me that you were so misunderstood. 'Muggy Mike' was your stage name and let's face it, the ladies did fall at your feet BUT everyone had this impression of you and you were literally the opposite you were one of a kind."