Gardaí say they are not treating the death of James Sheehan as suspicious.
A post mortem carried out on the remains of the teenager this morning found he died of natural causes.
The body of the 18-year-old was recovered from the Avoca River in Co. Wicklow yesterday.
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James had been missing since early Sunday morning after a night out in a club with friends.
It had initially been feared the teenager had been abducted.
A major search of the Arklow area involving Gardaí and over 100 local volunteers was launched.
Local Councillor Pat Fitzgerald says it has been hard time for all involved.