BBC - Sir Richard Branson has said he is "heartbroken" over the death of his wife Joan aged 80.
The pair, who married in 1989, had three children and five grandchildren.
In a post on Instagram, the Virgin Group founder said his wife was his "best friend" and "guiding light".
"She was the most wonderful mum and grandmum our kids and grandkids could have ever wished for," the 75-year-old wrote.
The entrepreneur did not say what caused her death.
In his post, Sir Richard wrote: "Heartbroken to share that Joan, my wife and partner for 50 years, has passed away."
He added: "She was my best friend, my rock, my guiding light, my world. Love you forever, Joan x."
The couple married on Necker island, owned by Sir Richard, in the Caribbean and had three children, Holly, Sam, and Clare Sarah, who died after four days.
Paying tribute to his mother, Sam Branson described her as "the kindest, most loving, warm and abundantly generous woman to walk this Earth."
"I am so deeply grateful to have had the privilege of being your son and being able to call you mum," he added.
In 2018, Holly wrote in a blog that her mother was raised in the centre of Glasgow and worked in a pawnbroker's shop, and, later, at a London bric-a-brac store in Portobello Road in west London.
She said it was there that her father first fell in love with Lady Branson and "turned up at the shop every day for months, buying stuff he didn't want or need."
Holly described her mother as "a stay-at-home mum who was (and still is) always there with a hug, inspiring words of wisdom, and a beautiful, welcoming smile."
In a blog to celebrate their wedding anniversary five years ago, Sir Richard said he "fell for Joan almost from the moment I saw her".
"Joan has always been a steady source of wisdom and has played no small part in some of my better life decisions," he added.
Sir Richard is one of the UK's most successful businessmen.
He founded Virgin Records in the 1970s, before his group expanded into other industries including air travel, broadband and space tourism.