Shane Burke, 19, tracked mum Rose Bestall, 35, using Facebook and organised a physical reunion soon after.
It took only a few weeks before Burke, from Manchester in England, realised his feelings had changed and he confessed them to Bestall, who was living in nearby Surrey.
“The confession left me with a massive dilemma,” she told Sunday People.
“I knew Shane’s feelings were completely inappropriate but I had searched for him for so long and I didn’t want to push him away again.”
The 19-year-old said the minimal age difference became a factor in his attraction.
“She is only 15 years older and I started to think of her in a romantic way,” he said.
“It was a very confusing time but I’m so lucky she was understanding.”
Burke believes he suffers from the psychological condition called genetic sexual attraction – a condition that occurs when a person becomes attracted to a biological relative they meet in adulthood.
“I now understand I was overcome by feelings of love for Rose,” he said.
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Bestall was only 15 when she gave birth to Burke and had him taken into care.
“Social services said I was too young to care for baby. I was distraught,” she said.
Burke was fostered out with Bestall still being allowed supervised visits until he was adopted.
Bestall now lives with her 33-year-old husband Darryl and their four younger children.
The 35-year-old said she refused the possibility of their relationship developing into something else.
“I told him I loved him unconditionally as his mum but our relationship could never be anything else,” she said.
“Thankfully he understood and we’re working on a normal relationship.”
The two were said to have bonded over a love of karaoke and often found themselves singing together in pubs.